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For: 2010 and Type: ALL these are the cases :

We have 58 events/cases to display for 2010 and Type: ALL

2010-12-31

A surge of warm humid air into the central United States produced severe weather and tornadoes on 31 December 2010. There were 17 reports of severe weather on the 30th and 126 reports of severe weather on the 31st to include 44 tornadoes. The tornadoes in Missouri resulted in several fatalities. All the severe weather occurred on 31 December but due to 24 hour reporting times, 17 reports appear on 30 December 2010. The severe storms occurred in the warm surge ahead of a cold front. The warm surge brought an end to a prolonged period of cold weather and brought unseasonable warm moist air into the Midwest and eastern United States. The precipitable water anomalies were 2 to 3 above normal and the 850 hPa temperatures were 1-2 above normal in the warm sector. The early spring-like temperatures and moisture spawned the severe weather outbreak.

2010-12-28

Severe, if not historic, flooding affected northeastern Australia in late December 2010. The state of Queensland was heavily impacted by the heavy rainfall and resulting floods. The flooding swelled rivers making them visible on high resolution satellite imagery, closed roads and rail lines, and affected over 200K people. The rainfall was associated with Tropical Cyclone Tasha and a trough of low pressure. These systems pushed high precipitable water into the region where precipitable water anomalies were over 2 above normal. Strong southerly winds produced 4 to 6 moisture flux anomalies into central Queensland. This case is good example on the use of standardized anomalies to diagnose situations conducive to heavy rainfall and the value of extreme moisture flux anomalies in identifying meteorologically and climatologically significant heavy rainfall events

2010-12-26

Overview of the East Coast Winter storm of 26-27 December 2010. Also known to some as the post-Christmas Blizzard of December 2010. Standardized anomalies are used to put the storm in perspective. Forecasts from NCEP ensembles and models are shown to illustrate the predictability issues with this storm. The negative NAO may have contributed to the potential for an ECWS despite the strong La Nina. Key words: anomalies; ensembles; snow.

2010-12-19

A surge of high PW air that persisted for several days and an enhanced eastern Pacific jet brought heavy rain to southern California with heavy snow at higher elevations. The system produced record rainfall at many locations and over 17 inches at one point in Ventura County (Fig. 1). The multi-day snowfall totals showed some locations received in excess of 100 inches and in one instance in excess of 200 inches of snowfall. This was an impressive precipitation event over southern Californian interior portions of the western United States. The surge of high PW air into southern California and the strong jet are more common in El Niño than in La Niña years. Not all La Niña’s are created equal. The data presented here imply that the GEFS predicted the overall pattern quite well and thus produced large QPF amounts. Clearly, the GEFS under predicted some of the incredible rainfall and snowfall amounts indicated by observations. This was clearly a significant HIWE with heavy rains and snow. The large anomalies indicate that this event was both meteorologically and climatologically significant. Clearly, the huge snowfall and rainfall totals will be hard to beat records and they will impact the local climatology.

2010-12-08

The data shown here imply that a deep upper-level disturbance (Fig. 3) and a ridge to the west allowed a surge of high PW air from lower latitudes into southern Australia. The strong mid-latitude wave and the deep tropical moisture produced heavy rainfall and flooding over southern and particularly southeastern Australia. This is another good example on the value of standardized anomalies (Grumm and Hart 2001; Hart and Grumm 2001; Graham and Grumm 2010) characterized a potential significant high impact weather event.

2010-12-07

A prolonged lake effect snow (LES:Hill 1971;Niziol 1987;Niziol et. al 1995;Reinking 1993 ) brought several feet of heavy snow to LES prone areas of Ohio, Pennsylvania and New York from 4 to 9 December 2010 (Fig. 1). The heavy snow associated with the event represents a high impact weather event (HIWE) affecting the I-90 corridor and at times extend southward to I-80 in Pennsylvania. During this event, the heaviest snow fell along the southeastern shores of Lake Ontario, near Oswego and Syracuse, New York. The bands of snow extended to the southeast into the eastern Finger Lakes and Catskill region of New York State (Fig. 2). DeWitt, Syracuse, and Fenner New York all received over 50 inches of event total snowfall. The data shown here suggest standardized anomalies (Hart and Grumm 2001;Grumm and Hart 2001) may have provided insights into the impact of this event. The sustained anomalous 850 hPa temperature, winds, and 500 hPa heights in the analyses and forecasts may have hinted of meteorologically and climatologically favorable pattern for a significant LES event.

2010-12-01

A deep trough brought a surge of anomalously high PW air into the eastern United States on 30 November through 1 December 2010. This plume of high PW air produced a significant severe weather event to include several late season tornadoes and heavy rainfall in the Mid-Atlantic and northeastern United States. The anomalies of key fields showed a pattern consistent with heavy rainfall in the eastern United States. This high impact weather event (HIWE) was generally well predicted by the NCEP ensemble forecast systems. The strong south-to-north flow over the eastern United States and associated of plume of high PW air is a classic Maddox-Synoptic heavy rainfall event type. As shown in Table 1, Synoptic rainfall events are the dominant heavy rainfall event type in the Mid-Atlantic Region during the month of December. This event will likely be a top-5 event for the month of December in terms of heavy rainfall. The number of points in the Mid-Atlantic region to exceed flood stage by date is shown in Table 2. These data are limited to events in December and only the top 21 events are shown. Many flood events span several days and a daily value may under represent a multi-day flood event. But these data illustrate, with 18 confirmed points over flood stage on 1 December 2010 that this event will likely move into the number slot displacing the December 2003 event. From a daily perspective the 13 December 1983 event (Grumm 2010) had the most points go over flood stage (31), however, the snow melt and rain floods of December 1950, a multi-day event with 3 entries in Table 2, was the most significant December flood in term of points over flood stage.

2010-11-23

A surge of tropical moisture (Figure 1) over the western flank of an anomalously strong and poleward shifted subtropical ridge (Fig. 2) produce rain over portions of Alaska on 22-24 November 2010. Liquid rainfall over inland regions of Alaska is rare during the cold season. Thus rainfall amounts approached record levels in many locations. Temperatures were much above normal, as much as 25F above normal. Barrow went above freezing. The cold ground caused freezing rain. In Fairbanks, the rain froze on the roads and exposed ground until the ground temperatures rose above freezing. Rain and freezing rain in interior Alaska are unique events. Fairbanks had over 0.60 inches of rainfall, one of the largest winter season rainfall events on record. The record event occurred on 20 January 1937 when 0.99 inches of rain fell on the city. Several other locations set daily precipitation records. True freezing rain, with ice on trees and power lines is also a relatively rare event. The last true freezing rain events in Anchorage were observed in 1995 and 1980. This paper will document the rare Alaskan warm rain event of 22-24 November 2010. The focus is on the anomalous pattern that produced the unique conditions and NCEP GEFS forecasts of the event

2010-10-26

A deep extratropical cyclone (Fig. 18) affected much of the continental United States from 25-27 October 2010. The central pressure of this storm surpassed several notable historic storms (Table 2), such as the Superstorm of March 1993, the Cleveland Superbomb of January 1978 and the Columbus Day Storm of October 1962. Each of these storms was more memorable for the high impact weather produced than the low pressure values associated with them. Based on the data in Table 1, this storm did not set a new extratropical cyclone record for the continental United States. The event of October 2010 will likely be remembered for the large multi-day severe weather event is initiated and its relatively predictable nature. The deep pressure center alone does not make for a memorable storm. The impacts on the public and the perceptions of those affected make lasting impressions in the minds of those affected. The wind and power failures with the Columbus Storm; the cold, snow and blizzard conditions associated with the Cleveland Superbomb make these events lasting and memorable. Similarly the high impact Superstorm of 13-14 March 1993 with the significant severe weather event and record snows make this a memorable storm from Florida to Maine. Key words: Pressure standardized anomalies ensembles.

2010-09-30

A slow moving north-south oriented frontal boundary and surges of tropical moisture along this boundary produced heavy rainfall in the eastern United States. Rainfall amounts over 4 inches were common from Virginia into eastern Pennsylvania. A broad area of 4 to 5 inches extended from North Carolina into Pennsylvania with embedded areas of over 10 inches of rainfall (Fig. 1). Maximum estimated rainfall as of 7 PM 30 September was 15 inches in North Carolina. North-south frontal systems with surges of high precipitable water air in the warm sector typify the Maddox Synoptic heavy rainfall events (Maddox et al. 1979). This event met this criteria. The interaction of this event type has historically produced some of the most significant heavy rainfall events in the Mid-Atlantic region. This record events, the interaction of Maddox-Synoptic Pattern with a tropical system is termed a Synoptic-Tropical event. This is simply a hybrid of the more generalized Maddox-Synoptic Event type. An aspect of this rainfall event of interest is the interaction the remnant circulation of short-lived tropical storm Nicole. The surge of tropical moisture up and ahead of the general north-south frontal boundary were critical in the heavy rainfall. This paper will document the pattern which produced the record rainfall of 30 September 2010. The goal is to show the pattern the forecasts of this pattern. The forecasts are used to relate back to the high probability outcome which was for widespread heavy rainfall. A connection is made showing the values of the pattern and its rarity and the confidence in the outcome, in this instance the high probability of heavy rainfall.

2010-09-27

A tornado in Paradise, Pennsylvania. Short-lived tornado of EF0 intensity affected the Vintage road area of Paradise. The tornado spun-up in a north-south rainband.

2010-09-23

Heavy rains impacted the upper Midwest on 23-24 September 2010 (Fig. 1). The heaviest rain fell between 1800 UTC 22 September through 1800 UTC 23 September 2010. The initial heavy rainfall was near the border if Iowa and Minnesota and then moved northward. The heavy rainfall was associated with convection. There were numerous reports of severe weather over Nebraska, Iowa, and southern Minnesota during the onset of the event. Most of the severe convection was on 22 September (Fig. 2). It will be shown that the pattern for this event was generally well predicted and thus the models and ensemble forecast systems (EFS) showed a high probability of heavy rain. The details remained elusive in this case. In this, the NCEP models and EFS clearly showed a bias placing the heavier rainfall north and west of the region where it was observed. This general northwest bias is a common error in many heavy rainfall events

2010-09-07

Tropical storm Hermine developed in the Bay of Campeche on 6 September and moved northward. The storm produced rain over the western Gulf (Fig. 1) and portions of Mexico before providing heavy rainfall and tornadoes to Texas (Figs. 2 & 3). The circulation with Hermine clearly brought strong winds, high PW values with high PW anomalies into Texas. The heavy rainfall areas were relatively well defined by the area of above normal PW air and the strong low-level 850 hPa winds (Figs. 7 & 8). The 850 hPa winds were near 6SDs above normal at times in the region of the heaviest rainfall. The heaviest rainfall over Texas was well aligned with the areas of high MFLUX (Fig. 9). MFLUX anomalies were slightly higher than 6SDs above normal at times near the areas where the heaviest rain was observed. The crude UPD data suggested that a large area of east-central Texas received over 5 inches of rainfall and up to 10 inches of rain was observed locally. Forecasts suggest that the surge of high PW air and thus the potential for heavy rainfall was captured by GFS, NAM, and SREF forecasts initialized at 4 September 2010. Early forecasts were not shown here. But the signal and high QPF potential were well predicted in the NCEP guidance

2010-09-01

The summer of 2010 will be remembered as one of the hottest summers in recent memory over most of the eastern United States, eastern Asia, and Russia (Grumm 2010). Global temperature data suggest that the period of June-August 2010 was one of the warmest on record in the northern hemisphere. NOAA reported that “The July worldwide land surface temperature was 1.03°C (1.85°F) above the 20th century average of 14.3°C (57.8°F)—the warmest July on record”. This record warmth came on the heels of a 3-month record warm period from April to June of 2010. Despite the warm temperatures, which began in January of 2010, the global sea surface temperature anomalies were decreasing as La Niña conditions set-up over the tropical Pacific Ocean for the summer months. By the summer La Niña conditions were fully in place and expected to dominate through the winter of 2010-2011. How these conditions impacted the United States is of interest here. This paper provides a summary of the significant sustained heat episodes which occurred across North America during the summer of 2010, with emphasis on the role and strength of the subtropical ridges associated with these heat episodes through the use of climatological anomalies. Anomalies...JRA25...heat wave.

2010-08-23

Heavy rain fell across the central Mississippi River valley (CMRV) and Northeast from the 20-23 August 2010 (Fig. 1). Both areas were associated with above normal precipitable water (PW). The rainfall over the CMRV was associated with convection ahead of a slow moving cold front. The Northeast rain was associated with an upper level low that became cut-off as it move out of the Ohio valley. The heaviest rain fell across northern and central Missouri as a bowing line segment moved through the area and new convection continued to fire up in its wake until the cold front finally moved through. The heavy rains occurred where a plume of high PW values surged northward from the Gulf of Mexico. PW values reached 2.2 inches at 0000 UTC 21 August 2010 at Davenport, IA which was the 8th highest value ever recorded. The rainfall in the Northeast was associated with the same frontal system as it moved east. The upper level low became cut-off over eastern Great Lakes and a surge of high PW values ahead of the cold front produced heavy rains across the Northeast. The 22/0000 UTC sounding at Pittsburgh showed PW values of 1.9 inches which exceeded +2SD. The low then moved over western New York and a strong southeasterly 850 hPa jet allowed a second surge of high PW air along the coast to filter into the interior Northeast. This paper will document the rainfall and the associated high PW which produced it. The goal is to demonstrate the value of anomalies in forecasting heavy rainfall events.

2010-08-20

Heavy rains caused flooding over northeastern China and adjacent North Korea 19-21 August 2010. The heavy rains fell on the poleward side of a strong subtropical ridge (Fig. 1) with a surge of above normal precipitable water into the region (Fig. 2). This ring-of-fire like pattern is often associated with heavy rainfall in the United States. Additionally, this pattern and flood impact often are enhanced with strong subtropical ridges with 2-4SD above normal height anomalies. More than 250 000 people were evacuated in northeastern Chinas Liaoning Province. Evacuations and rescues were also reported on the south side of the swollen Yalu River in nearby North Korea. Flooding where rainfall amounts may have exceeded 300 mm (12 inches). The heaviest rains in North Korea were near Sinuiji. This paper will examine the conditions associated with the heavy rainfall. The focus is on the value of anomalies of key fields such as PW and PW anomalies and moisture flux to predict regions of heavy rain. Some model and ensemble data presented to deal with predictability issues.

2010-08-18

Heavy rain fell over the Gulf States, into the Tennessee Valley and in the Mid-Atlantic region from 17-19 August 2010 (Fig. 1). All three areas of heavy rainfall were associated with above normal precipitable water (PW). The rainfall over the Gulf and Ohio Valley was associated with a rejuvenated circulation of former Tropical Depression #5. The circulation was clearly evident as the system moved onshore late 16-7 August 2010 (Fig. 2). The heavy rainfall with the remnants of TD#5 fell mainly west of the track of the 850 hPa low but east of the surface cyclone over eastern Louisiana and western Mississippi (Fig. 1). Higher resolution data revealed a cyclonic pattern to the rainfall. The surge of high PW produced the second largest all-time PW (2.88 inches) value at Slidell, Louisiana on 1200 UTC 17 August 2010 and Jackson, MS set a new record high PW value (2.76 in) at 0000 UTC 18 August 2010. The old record was 2.57 inches set on 12 August 1987. Interesting all 10 of the record high PW values in Jackson were set in August (6) and July (4). The rainfall in the Tennessee Valley was also associated with the remnants of TD#5 as it interacted with a frontal system. The same general frontal system, with high PW air in it also produced the heavy rainfall in the Mid-Atlantic region. This paper will document the rainfall and the associated high PW which produced it. The goal here is to demonstrate the value of anomalies in forecasting heavy rainfall events.

2010-08-18

Heavy rain fell over the Gulf States, into the Tennessee Valley and in the Mid-Atlantic region from 17-19 August 2010 (Fig. 1). All three areas of heavy rainfall were associated with above normal precipitable water (PW). The rainfall over the Gulf and Ohio Valley was associated with a rejuvenated circulation of former Tropical Depression #5. The circulation was clearly evident as the system moved onshore late 16-7 August 2010 (Fig. 2). The heavy rainfall with the remnants of TD#5 fell mainly west of the track of the 850 hPa low but east of the surface cyclone over eastern Louisiana and western Mississippi (Fig. 1). Higher resolution data revealed a cyclonic pattern to the rainfall. The surge of high PW produced the second largest all-time PW (2.88 inches) value at Slidell, Louisiana on 1200 UTC 17 August 2010 and Jackson, MS set a new record high PW value (2.76 in) at 0000 UTC 18 August 2010. The old record was 2.57 inches set on 12 August 1987. Interesting all 10 of the record high PW values in Jackson were set in August (6) and July (4). The rainfall in the Tennessee Valley was also associated with the remnants of TD#5 as it interacted with a frontal system. The same general frontal system, with high PW air in it also produced the heavy rainfall in the Mid-Atlantic region. This paper will document the rainfall and the associated high PW which produced it. The goal here is to demonstrate the value of anomalies in forecasting heavy rainfall events.

2010-08-08

A strong subtropical ridge persisted over central Europe during most of the months of June, July and August 2010 (Fig. 1-3). The above normal warmth began in mid-June and persisted most of the summer. The strong subtropical ridge produced record warmth over many locations in central and Eastern Europe. Finland experienced a stretch of record warmth in July. Most of Western Russia had the hottest summer in record history . The heat over Russia produced many days where the high temperatures was 40C (104F) or greater. Russia clearly had a record warm summer with Moscow averaging near +18C and +16C above normal for the month of July and August. Under the subtropical ridge 850 hPa temperatures were 2 to 4SDs above normal over Russia during the month of July (Fig. 1b). The high temperatures combined with dry conditions (Fig. 1d) created massive fires across the country. Peat bog and forecast fires made the news during the months of July and August. The country is experiencing the worse drought since 1972. The conditions may have decreased Russian grain production by about 30% relative to 2009 levels. The government put a temporary grain export limit in effect until the full impact of the heat wave on grain production is known. This paper will document the large scale conditions associated with the eastern European and Russian heat wave of July-August 2010. The focus is on anomalies associated with key features. This is based on the work of Lipton and Grumm (2005) which showed the value of anomalies in identifying heat waves and warm episodes.

2010-07-26

Heavy rains brought flooding to portions of northeastern Pakistan in July and early August of 2010. Satellite rainfall estimates showed heavy rains over northeastern Pakistan and large portions of India during the month of July (Fig 1). It will be shown that there were two periods of heavy rainfall in Pakistan. Eastern Punjab province experienced heavy rainfall between 12-15 July and again later in the month. Later in the month heavy rains affected Bolachistan, Khyber-Pakhtunkhwa, Gilgit-Baltistan, and Punjab Provinces. The heavy rainfall earlier in the month may have set the stage for the flooding with the second period of heavy rainfall. meteorological context of the event is of interest here. Figure 2 shows the large scale pattern over central Asia from 0000 UTC 1 to 1800 UTC 31 July 2010. A weak trough is over the region with a large high-latitude over northern Europe (Fig. 2a). The 850 hPa temperatures show the warm air with the ridge over Eastern Europe, the high impact record heat event which affected Russia. Beneath the ridge, the precipitable water values were below normal likely contributing to the fire problems in Russia. But to the south the precipitable water values were above normal for the month of July (Fig. 2d). Finally, a strong subtropical jet with 1 to 2 standard deviation anomalies was focused across northern Afghanistan, Pakistan, India, and into northern western China. The jet core was over 32 ms-1 which was clearly above normally strong for the time of year. These data suggest a stronger than normal jet and higher than normal precipitable water, due to a strong monsoonal circulation; may have been related to the heavy rainfall in Pakistan. This paper will attempt to document and show the key meteorological features associated with his historic event. The focus here is on the pattern and anomalies as analyzed and forecast by numerical weather prediction. A few forecasts of the precipitation are presented.

2010-07-25

Heat wave ending severe weather event in the Mid-Atlantic region.

2010-07-21

A large subtropical ridge developed over the southern United States. This ridge split at times as short-wave energy moved over the top to the feature (Fig. 1 & Fig. 6). The interaction with flow over the ridge produced several significant severe weather events during the period. As the western Atlantic portion of the ridge retrograded over the southeastern United States, the low-level jet about the ridge strengthened. This produced a surge of moisture into the Midwest which in turn produced persistent organized convection and flooding from Iowa to Michigan (Fig. 7). The focus here is on the severe weather as the subtropical ridge pumped moisture into the central and eastern United States. The classic run-of-fire developed and produced some significant severe weather events, at times in places where large and widespread severe reports are often not very common. The focus is on the pattern and impacts mainly in the eastern United States

2010-07-12

Long duration heat wave affected central and northern Europe. The event set record highs in Finland and had temperatures near 40C in Germany. Classic event with close 5880m contour at 500 hPa and above normal 700 and 850 hPa temperatures in the heat affected regions.

2010-07-06

A large subtropical ridge built over the eastern United States from 3 to 7 July 2010. Warm temperatures with 2 to 3SD temperature anomalies brought a protracted heat wave to the eastern United States from 4-8 July 2010. Most locations had successive days of 90+ temperatures and many sites recorded 100+ temperatures on one or more days. An overview of the event and the pattern associated with the event is presented.

2010-07-01

Hurricane Alex ambled across the Gulf of Mexico bringing heavy rainfall to Texas and northern Mexico from 29 June to 2 July 2010 (Fig. 1). News reports implied as much as 750 mm (30 inches) of rain may have fallen in the hills of northeastern Mexico. Flooding and raging water were observed in Monterrey, Mexico. Monterrey lies on the eastern edge of the Sierra Madre Oriental Mountains. The higher peaks of the Sierra Madre Oriental reach 3250 to 3300 meters. The data in Figure 1 likely under sampled the rainfall in the mountains of Mexico west of Monterrey. In addition the rainfall, the storm brought high values of precipitable water (PW) into the region. Soundings and model analyses showed over 65mm of PW. At times the PW anomalies were over +5 standard deviations above normal. High PW air and large PW anomalies are often associated with record rainfall events, including land falling tropical systems. This storm was likely a textbook example of this association of heavy rainfall with high PW anomalies. This paper will summarize the pattern and the heavy rainfall associated with Hurricane Alex. The focus is on the patterns and anomalies that produced the heavy rainfall. Moisture Flux, anomalies, precipitable water.

2010-06-24

A large subtropical ridge over the southern United States (Fig. 1) brought an extended period of severe weather to the north Great Lakes and eastern United States from 20-24 June 2010. The persistent subtropical ridge pushed warm moist air along and over the ridge which produced several severe events (Fig. 2). The most interesting event in the eastern United States was on 24 June when a cold front produced widespread severe weather from Pennsylvania to New England to include a rare tornado in Bridgeport, Connecticut. Figure 2 shows the classic ?ring of fire? appearance to the severe weather when compared to Figure 1. The events on 22 and 23 June both showed a classic anticyclone-arc about the persistent subtropical ridge. The ridge was progressive and the severe weather clearly shifted eastward with the ridge. The severe weather on the 23rd produced a series of lines with embedded rotating storms. These storms produced flooding, downbursts and tornadoes across northern Illinois, Indiana and Michigan. Figure 3 shows the 500 hPa pattern centered on 0000 UTC 23 June 2010 and all the severe weather observed during the period. The lower panel shows the precipitable water (PW) and precipitable water anomalies. These data imply that the severe weather was generally confined to the area north of the massive subtropical ridge (Fig. 3a) and in the plume of high PW air which wrapped around this feature. Note the PW anomalies are near normal within the subtropical ridge. This paper will summarize the pattern and severe weather of 20-24 June 2010. The focus is on the severe weather over Pennsylvania and surrounding States. The broader context in time is presented due to the value of knowing the patterns which might aid in better anticipating severe weather. Anomalies...subtropical ridge...severe convection.

2010-06-15

Extremely heavy rainfall led to a historic fatal flash flooding event across much of the Var Department in Southern France during the middle on 15-16 June 2010. This heavy rain event was influenced by a deepening 500 hPa closed low and cool mid-tropospheric temperatures stationed over the Iberian Peninsula, coupled with anomalously high precipitable water on the eastern side of the low centered over Sardinia (Figure 1). Rain fell over Southern France, mainly between 0000 UTC 15 June and 0600 UTC 16 June. In instability with the short-wave triggered convection which was able to tap warm moist Mediterranean air which was advancing northward ahead of the short-wave. This warm air was moving over the western foothills of the Alps, thus there was orographic lifting involved with the event. Over 40 cm of rain, or the equivalent of 6 months of the average annual rainfall, was observed during this event just to the south of Draguignan, France (Figure 2). This rapid accumulation resulted in the region’s worst flash flooding since 1827. The flooding resulted in the deaths of at least 25 people . This paper will show the large scale conditions associated with the heavy rainfall and flood event of 15 June 2010. The focus is on the climatic anomalies of key fields that may have aided in forecasting this event. Regional scale model simulations are shown to show how high resolution models can aid in defining potential areas of heavy rainfall.

2010-06-14

Heavy rainfall fell over Oklahoma and Texas on 14 June 2010 (Fig. 1). Over 128 mm (5 in) was observed in and around Oklahoma City with 256 mm (10 in) observed in the high resolution rainfall data. Reports of 12 inches were reported by public spotters. During the Oklahoma City heavy rainfall, another area of heavy rain clearly impacted the Texas Panhandle with 192 to 256 mm of rainfall too. The second heavy rainfall area did not have the impact that the heavy rainfall in Oklahoma City had. The 6-hourly data showed that the heavy rainfall over the Texas Panhandle occurred between 13/1800 and 14/0600 UTC (Fig. 2) and the heavy rain in Oklahoma City occurred between 14/0600 and 14/1800 UTC. The heaviest rainfall over Oklahoma City occurred between 14/1200 and 14/1800 UTC. This matches news reports citing heavy rainfall around 1100 AM CDT. Anomalies showed high PW air around a strong anticylone. Convection developed and tapped this high PW air. Floods 14 June 2010.

2010-06-11

Training convection associated with deep moisture and a strongly southerly low-level jet brought heavy rainfall to central Arkansas 10-11 June 2010. The heavy rains triggered flash flooding along two rivers in southwestern Arkansas. The flooding along these rivers killed around 16 people . Estimates suggest the water level in the rivers rose at 6-8 feet per hour. The Little Missouri River at 3.81 feet at 0200 IS CDT and crested at 23.39 feet at 530AM CDT. The National Weather Service in Little Rock, Arkansas (KLZK) issued flash flood warnings for the region and posted a summary of the event. The radar and observations suggested that 6.78 inches fell at Hopper in Montgomery County, 6.55 inches at Glenwood, in Pike County and 5.64 inches at Mount Ida. The KLZK radar suggested some very heavy rains also fell over northeasternmost Texas. Figures 4-6 and Figure 12 showed the potential for heavy rainfall about 1/5 to 1/3 of the observed amounts. These course 32km data were not likely to get the convective processes correct. And they did not. Neither did the high resolution models. The large QPF, potential for convection and back building were clues to be vigilant. The 2 to 2.5SD PW air with strong southerly flow were clues that heavy rainfall could be significant. The most workable clue was the persistent forecasts of 2 to 3SD PW anomalies right over Arkansas in an environment conducive for heavy rainfall.

2010-06-06

A rapidly deepening surface cyclone raced across the Midwest and into New England on 5-6 June 2010 (Fig.1). This storm system produced severe weather (Fig. 2). Tornadoes were observed on the 5th from Iowa to Ohio. The severe weather, mainly in the form of wind damage, raced across Pennsylvania early Sunday morning then across New York and New England on 6 June 2010. The severe weather and tornadoes were well aligned if not concentrated along the axis of the anomalous 850 hPa jet. RUC or NARR data might show, in 3-hourly increments, the strengthening jet between 05/2100 and 06/0300 UTC. The 6-hourly NAM and GFS cannot resolved these features unless a 3-hour forecast is employed. The NAM CAPE (Fig.6) compared to the 850 hPa winds (Fig. 5) suggest that the lack of surface based CAPE modulated the convection considerably. With both high CAPE and the strong low-level jet, deep convection was able to develop from Illinois to western Pennsylvania. These storms were able to persist and develop into more lasting supercell storms. Over Pennsylvania, despite the high shear, the storms could not organize and thus persistent thunderstorms were hard to evolve The radar data from KCLE and KCCX revealed that the storms in Ohio, with high CAPE and strong shear were large persistent storms with well defined mesocyclone. The storms in Pennsylvania lacking large CAPE lacked big updrafts and thus could not persist nor develop persistent and deep mesocyclones. This limited the threat and observations of tornadoes in Pennsylvania and likely points farther to the east

2010-05-26

A large subtropical ridge developed over the eastern United States during the week of 24 May 2010 (Fig. 1). This feature was associated with some interesting, if not unique weather over much of the eastern United States and Canada. Warm moist air transported poleward of the ridge produced convection and mesoscale convective complexes over Canada which moved over northern New England. Dry conditions and lightning produced fires in Quebec. Under the ridge, the warm air produced record high temperatures over southern Canada and the eastern United States (Table 1). At the height of the event, daytime highs exceeded 90F from Chicago to Hartford. Many high temperature records were set in central New York and southern New England on 26 May 2010. Locations in Ontario and Quebec saw high temperatures in the 80s and 90s from 25-27 May 2010

2010-05-25

A deepening mid-tropospheric cyclone moved over New Zealand on 24-25 May 2010 producing heavy rainfall and flooding. The eastward propagating tapped an AR of deep moisture. The plume of high PW in this AR contained PW values over 3SDs above normal. Upon interacting with the terrain of New Zealand, this warm moist air mass produced widespread areas of 100 to 150 mm of rain. The rain led to flooding. The surge of high PW and the strong poleward 850 hPa winds are common in the eastern United States with heavy rainfall events. It would appear that a similar mechanism and pattern can produce locally heavy rainfall across New Zealand. The archetype for this type of event and the terrain influence are quite common throughout the world and are rather well predicted by most numerical weather predictions systems. The NCEP GFS did respectable in terms of where the and when the heavy rain would fall. Get the pattern, get the precipitation. Additionally, the GEFS produced excellent forecasts for a global ensemble. These course systems tend to under predict high end QPF amounts and relative to there high resolution models. But they provide patterns and probabilities which in turn provide confidence in the forecasts.

2010-05-23

During the overnight hours and into the early morning of 23 May 2010 a north south oriented line of showers brought heavy rain from northern Virginia into southern Pennsylvania. Two areas of precipitation affected Pennsylvania. The precipitation was focused along to generally southwest to northeast geographically features, Blue Mountain and South Mountain. The heaviest rain fell in Pennsylvania fell over the westernmost features, Blue Mountain. One report of 6 inches of rainfall was reported near St Thomas near Blue Mountain. This locally heavy rainfall produced flash flooding and flooding along streams and creeks in southern Pennsylvania and Maryland. As shown in Figure 2, the heavy rainfall fell over a limited area.

2010-05-14

A cold front moving through the eastern United States on 14 May 2010 (Fig. 1) triggered a widespread severe weather event (Fig. 2). The event contained no tornadoes but many of the storms produced large hail. Hail was the dominant severe phenomena observed over the Mid-Atlantic region. Ahead of the frontal boundary, from New Jersey into Arkansas, high winds and hail were common. It will be shown that this was a southwesterly flow event (Fritsch and Giordano 1991). The key features included a large subtropical ridge over the southeastern United States with strong southwesterly flow along the western flanks of this feature. This southwesterly flow brought warm moist air up the Ohio Valley and into the Mid-Atlantic region. The deep moisture and instability aided in the development of large storms. Over Pennsylvania persistent storms with moderate to strong mid-level rotation were observed. It appeared that each supercell thunderstorm produced severe weather in the form of large hail and damaging winds. Hail reports were more numerous than wind reports. Due to the strong winds, there were reports and pictures of hail damage to siding. Windblown hail clearly can pierce vinyl siding with ease.

2010-05-10

A much anticipated tornado outbreak affected the southern plains during the afternoon and evening hours of 10 May 2010. There were 42 tornadoes in Oklahoma and Kansas and over 158 reports of severe weather over the southern plains (Fig. 1). The large scale pattern associated with this event included a upper-level jet over the western United States (Fig. 2a), a strong southerly jet over the southern plains (Fig. 2b) a surface cyclone over eastern Oklahoma (Fig 2c)and a surge of moist air over the region (Fig. 2d). The precipitable water (PW) field showed a north-south oriented dry-line over the region with -2 standard deviation below normal PW anomalies west of this feature. The classic and well known ingredients for a severe weather event were all in place. It will be shown that these favorable large scale conditions were well predicted by the NCEP ensemble forecast systems (EFS) and the higher resolution models. Thus, this event was well anticipated several days in advance and thus the media and VORTEX-2 teams were in place to document the event. NCEP?s Storm Prediction Center (SPC) issued a rare high risk for severe weather over the region which was hardest hit by the severe weather on 10 May 2010. This paper will document the large scale conditions and anomalies associated with the features which produced the severe weather and tornadoes on 10 May 2010. Forecasts of these features and anomalies are then presented. This case will likely be the subject of additional more comprehensive research in the near future. High resolution datasets to include high resolution radar data were likely successfully gathered by the VORTEX-2 teams for this event.

2010-05-02

A devastating heavy rainfall event affected the Mid-Mississippi Valley (MMV) from 1-3 May 2010. The heavy rain and associated severe thunderstorms killed 29 people in the impacted region. As shown in Figure 1, the heaviest rains extended from northwestern Mississippi across western Tennessee and into southwestern Kentucky. Western Tennessee had the heaviest rainfall with over 200 mm inches in the gridded datasets and reports of over 400 mm based on spotter reports. The City of Nashville was devastated by floods which closed the historic district and impacted famous sites such as the Grand Old Opry House. Nashville set a single day record on 2 May 2ith 7.25 inches exceeding the record 6.60 inches set on 13 September 1979. This followed the now third wettest day on record, 1 May 2010 when 6.32 inches of rain was observed. The 2-day rains made May 2010 the wettest May on record for the city. The 2-days of heavy rainfall set many new record rainfall records across portions of western Tennessee and Kentucky. The largest report to date was 17.73 inches at Camden, Tennessee. Bowling Green, Kentucky, a location with over 140 years of records, set a 2-day record with 9.67 inches of rainfall. This paper will document the historic and devastating rainfall and flooding over the MMV on 1-2 May 2010. The focus is on the pattern and anomalies associated with this meteorologically and climatologically significant event. Some forecasts from the NCEP models and ensemble forecast systems (EFS) are presented to show the value of ensembles in the forecast process.

2010-04-24

Southern US fatal tornado event. Widespread severe weather on Saturday 24 April 2010 produced many reports of severe weather from the Gulf of Mexico to the Ohio Valley. High CAPE and shear led to supercells and many tornadoes. Tragically several cells caused fatalities. The event was relatively well predicted in terms of the instability and shear over the locations of the severe weather and tornadoes

2010-04-16

A belt of anomalously strong westerly winds in excess of 40-50 kts preceded a frontal boundary as it swept across Pennsylvania during the afternoon and evening hours of Friday 16 April 2010. Anomalous winds at 850 hPa (Fig. 1) and the 850 hPa u-wind anomalies clearly defined the area of severe weather (Fig. 1). Ahead of the front unseasonably warm air was over the region. These data clearly show that the strongest winds and severe weather occurred ahead of the cold frontal feature at 850 hPa. Vertical wind profiles showed that these strong winds extended to 1500 to 2500 feet above ground level. This favored high winds should convective elements grow larger enough to tap the strong winds aloft. In addition to the strong winds, there was relatively dry air at lower levels. This produced relatively high lifting condensation levels (LCL) and an inverted-V like sounding (Fig. 2) favoring cooling of any thunderstorm induced downdrafts. This had the potential to add 20-30 percent to the environmental winds transported to the surface by convection. Straight-line winds were the main problem. Reports indicated at the height of the event over 75 000 homes lost power due to downed power lines. A unique aspect of this event was the number of measured winds over 50 KTS at METAR sites such as Latrobe, Johnstown, Altoona, and Middletown all reported gust over 50 KTS. Several other sites recorded winds between 40 and 49 KTS including Indiana, University Park, Muir Field, and Lancaster. Altoona recorded a peak wind of 69KTS (79MPH). A few spotter also reported winds over 50 KTS. But most of the wind information came in from reports of downed trees, downed power lines, roofs blown off homes, and a few collapsed or semi-collapsed buildings.

2010-04-08

The first severe weather event of the 2010 season struck central Pennsylvania on the afternoon of 8 April 2010. The colder air behind this front marked the end of what had been an extended period of near record warmth. Most of the severe weather was in the form of wind damage (Fig. 1) and occurred ahead of a cold front. As shown in Figure 1, the cold front produced severe weather form southern New York southward into Florida. The tornado activity was confined to the States of Alabama, Georgia, and Florida (red triangles). This is not surprising as the data in Figure 2 suggest Pennsylvania averages about 1 tornado per year during the month of April since 1950. A mesoscale convective vortex (MCV: Figure 3) like structure developed as the system lifted to the north and east. The main line was east of Williamsport by about 2200 UTC. Linear elements and a weak bow echo characterized this event.

2010-04-05

A prolonged period of unseasonably high temperatures affected the eastern United States from 2-8 April 2010. The event followed an unseasonably warm March over the same region. Many record highs were set from the Ohio Valley into the northeastern United States during the 8 day period. Pittsburgh, Pennsylvania set a new record daily high (85F) and earliest high temperature so early in the season on Friday 2 April 2010. A weak cold front limited the warm on the 4th, which was a relatively cooler day over most areas. As impressive as the high temperatures were, overnight lows were typical 1 to 2 standard deviations (SDs) above normal at many locations during the event. Figure 1 shows the daily highs and lows in State College, PA. The overnight lows were 1 to 2SDS above normal from 2-8 April 2010. Daily high temperatures approached 3SDs above normal during much of the same period. Early season warm episodes are not uncommon. In March 2006, a warm episode saw temperatures rise into the 70s to around 80 from 10-13 March 2006. Other notable early warm episodes include the event include 25-27 April 2009, 16-19 April 2002, 24-29 April 1990, 12-13 April 1977 and the event of 16-21 April 1976. With early season reading in the 90s, the 16-21 April 1996 is often considered the comparative gold standard of early season warm episodes. This paper examines the heat episode of 2-8 April 2010 and compares it to previous events. Ensembles...anomalies...predictability.

2010-03-30

The second of two significant nor?easters affect the northeastern United States struck on 30-31 March 2010. The combined effects of these two storms, the first occurring on 13-14 March 2010 led to many locations in southern New England setting new monthly rainfall records. The second storm produced record flooding in Rhode Island and Massachusetts. This devastating heavy rainfall event had all the signals indicative a significant heavy rainfall event. Based on the work of Stuart and Grumm (2009) and Maddox et. al. (1979) this event possessed to classic characteristics of a heavy rainfall event. Early in the event the sharp north-south frontal and moisture zone had a synoptic event type pattern. The atmospheric River (Neiman et al 2008) along the coast brought heavy rains to the region. The PW surge had above normal PW anomalies and above normal v-wind anomalies. It will be shown that as the surface cyclone rolled up the frontal boundary, the event transitioned into a frontal system (Maddox et al 1979) and the strong easterly winds focused the heavy rainfall in the region of this strong and anomalous easterly jet (Stuart and Grumm 2009). This event had persistent and anomalous moisture and anomalous southerly and then easterly flow, all the ingredients for a significant heavy rainfall event (Doswell et. al 1996). Ensembles..Anomalies..heavy rain....flood

2010-03-20

Subtropical ridge and related subtropical jet (STJ) with large height anomalies brought surge of warm air and warm episode to southwest Asia and India. May be relationship ENSO positive event and stronger than normal STJ which may have produced the strong ridge and resulting earlier than normal surge of warm air into the Indian subcontinent.

2010-03-13

An historic nor?easter affected the East Coast of the United States on 13-14 March 2010. The storm will be remembered for heavy rainfall (Fig. 1), flooding, strong winds, and the coastal surge . Hurricane force wind gusts were reported at Kennedy International Airport (KJFK) around 0000 UTC 14 March 2010 when wind gusts reach 64KTS (74 mph). Islip had 54 KTS winds . The strong winds produced widespread power outages, downed trees, and produced coastal flooding due to a strong storm surge. This storm has been compared to several past storms. The nor?easters of 12-13 December 1992 and 07-08 January 1996 storms both produced strong storm surges along the East Coast. Unlike this storm, these storms produced areas of heavy snowfall. Another similar storm, which produced heavy rainfall, was the 3-4 March 1993 event. All of these storms had strong easterly winds with significant u-wind anomalies north of the cyclone. It was in this general area where these storms produced the most significant impact. The 850 hPa winds and u-wind anomalies during the peak of the 13-14 March 2010 nor?easter are shown in Figure 2 The comparative storms all shared some common characteristics. The key feature they all had in common was strong 850 hPa u-winds with u-wind anomalies in the -5 to -6SD range. These common features, often well predicted could be leveraged to improve rating and evaluating East Coast Winter storms. Ensemble forecasts compared to climatology and model climatologies could be leveraged to rate nor?easters based on ensemble forecasts. An operational storm rating system from 1 to 5 could be used. Threats for key features could be made in relation to snowfall threats, rainfall threats, high surf and coastal flooding threats and high wind threats.

2010-02-28

A destructive late winter storm pounded the Iberian Peninsula, the French Coastline and other locations of Western Europe from France to Germany. A collapsed sea wall in France was the cause of the majority of fatalities associated with this event. The event was relatively well predicted by the NCEP GEFS and by the European Center for Medium range forecasting ensemble prediction systems. The ECMWF Extreme Forecast Indices (EFI) indicated a high probability for high wind and heavy rainfall . Clearly the NCEP EFS predicted a strong storm with anomalous winds and the potential for locally heavy rainfall. The data presented here suggest that an anomalous cyclone with deep pressure, strong winds, with significant low-level wind anomalies provided clues and signals for a potential significant event. If the simple anomalies derived from climatology showed such an event it is not surprising that the ECMWF EFI, based on the EFS?s built in climatology could detect and predict this storm. EFI ensembles anomalies France

2010-02-26

Strong nor?easter impacted the northeastern United States on 25-26 February 2010. This storm produced record snows over portions of northeastern Pennsylvania and eastcentral New York State (Fig. 1a). East of the storm, heavy rains were observed with over 200 mm (8 inches) in southeastern Maine (Fig b). In addition to the heavy snow and rain, the storm produced gale force winds and wind gust reaching hurricane force (Fig. 2). A summary of the larger snowfall amounts and rainfall amounts are summarized in Tables 1 & 2 respectively. This storm is called the upside-down nor?easter due to the surge of warm air north and east of the low-level cyclone center. This produced an interesting situation where rain was observed hundreds of kilometer north of areas receiving heavy snow. Through much of the storm evolution, Albany, NY was 37F with rain while heavy snow affected New York City. New York City would receive over 20 inches of snow during the event. This paper presents and overview of the inverted nor?easter of 25-26 February 2010. It was a powerful and memorable extratropical cyclone, one of many that contributed to the record breaking snowfall observed in many locations in the eastern United States during the highly negative Arctic Oscillation winter of 2009-2010. Snowicane...historic snow....anomalies...ensembles

2010-02-24

A winter storm developed along the East Coast and brought heavy snow to interior New York and western New England. Snowfall amounts of over 2 feet were observed in portions of the Hudson Valley and the mountains of western Massachusetts and Vermont. East of the 850 hPa cyclone center heavy rain dominated with some areas of southern New York and New England receiving around 2 inches of total rainfall. This event was a classic winter storm relative to where the snow fell relative to the 850 hPa low (Goree and Younkin 1966). The snow fell north and west of the track of the 850 hPa cyclone. Rain was observed on the east side of the 850 hPa cyclone track. The surge of high PW air into the storm and the -3 to -4 SD u-wind anomalies (Stuart and Grumm 2006) were clues to a potential heavy rainfall event and heavy snow on the cold side of the storm. This storm and the pattern of precipitation around it were what one might expect based on the anomalies of the 850 hPa winds and PW fields. A meteorological significant event was implied by the anomalies and observations suggest that such an event occurred. With mean monthly rainfall on the order of 3-4 inches over much of the affected area, a large swath of 1.5 to 2 inches of precipitation implies that some sites may have received as much as 50% of the monthly rainfall in one event. Thus was also a climatically significant event.

2010-02-20

A devastating and deadly rain event impacted the Madeira Islands (Fig. 1) on 20 February 2010. The heavy rain fall on the Island caused flooding and mudslides. Around 50 people perished in this event. The heavy rainfall was associated with a plume of deep moisture which came across the Atlantic Ocean and took aim at the Islands (Fig. 2 & 3). The precipitable water (PW) anomalies from the ?rum-runner express? were on the order of 4 to 5 SD deviations above normal. Clearly, an atmospheric river of deep moisture (Neiman et al 2002 and 2008) was associated with this devastating rainfall event. The rainfall was associated with a strong westerly 250 hPa jet (Fig. 10a & 11a) and strong southwesterly flow (Figs. 10c & 11c) which brought a surge of high PW air into the island. This atmospheric river of high PW air had 4 to 5 SD PW anomalies with its core. The implied upslope southwest winds would have on the islands terrain features were likely contributed to the devastation.

2010-02-18

After a cold surge and some record lows in the southern Plains on 10 February, a surge of above normal air in conjunction with a strong 500 hPa ridge (Fig. 2) produced a rapid thaw over most of the eastern United States during from 13-18 February 2011. The thaw in the Mid-Atlantic resulted in a 2-day period of warmth, with record high temperatures in the 60s across Pennsylvania on the 19th. The combination of warm air, moist air, and gusty winds substantially eroded the snow cover over large portions of the eastern United States. A cold front moved across the eastern United States on the 18th and early on the 19th. Strong winds along and behind the frontal boundary reached the surface. High wind warnings were posted in advance of this system. These warnings were likely based on the strong winds and above normal winds in the model and ensemble guidance. The NCEP SREF showed nearly a 100% chance for 3s above normal 850 hPa winds (Fig. 10) above normal behind the front, where isentropes are typically steeply sloped and thus may allow winds from 850 to 700 hPa to reach the surface. The high winds caused power outages and fanned wild fires in the Mid-Atlantic region. The winds also ushered in cold air, ending the warm episode. The 500 hPa height and temperature anomalies captured the potential for this warm event in the forecasts and analysis. The 850 hPa wind anomalies appeared to capture the potential for the snow melt during the warm period and the strong post-frontal winds

2010-02-12

A surface cyclone tracked across Mexico and the Gulf of Mexico (Fig. 1) producing snowfall from Texas to Florida as it tracked eastward (Fig. 2). Several locations, including Dallas/Fort Worth set a record snowfall for the month and for a single 24 hour event on 11 February 2010. The 11.2 inches at DFW beat the old record of 7.8 inches set on 14 January 1917 and 15 January 1964. This was one of the largest snowfall events in Texas since the historic Christmas 2004 storm (Morales 2009 and Morales 2007) which produced as much as 13 inches of snow along the Gulf Coast on 24-25 December 2004. This storm produced 1.5 inches of snow in Brownsville, which was the first snowfall since 1899. Deep southern snows, though rare do occur. During December 1989 there was another deep southern storm which brought a White Christmas to many of the Gulf and southeastern States. This snow event occurred during a time of unseasonably low values of the Arctic Oscillation (Table 1) and a period of high latitude blocking (Rex 1950a&b). This general pattern has dominated the northern hemispheric winter of 2009-2010. This tends to push cold air and the storm track to the south. Combined with a an El Nino episode, which favors Pacific Storms moving into North America farther south is a good combination for cold and wetter conditions in the southern United States. The right combination of cold and precipitation occurred 11-13 February 2010. This deep southern storm produced measureable snow in all the southern States. On the morning of 13 February 2010 snow was reported in 49 of 50 States. The lack of snow on Mona Lao left Hawaii out of the snow party. This paper will document the historic Deep South snow event of 11-13 February 2010. The focus will be on the pattern and the anomalies of key fields associated with potential winter storms.

2010-02-10

A high impact East Winter Storm (ECWS: Hirsh et al 2000) brought heavy snowfall to the megalopolitan corridor of the northeastern United States on 10-11 February 2010 (Fig. 1). This storm set new snowfall records for the date at many locations. Had this storm occurred 24 hours later the record snow fall produced by the Megalopolitan Snowstorm of 11?12 February 1983 (Bosart and Sanders 1985) would have been difficult to top at many locations. This was the second significant, if not historic, snow storm to produce double digit snowfall in Washington (10.8), Baltimore (19.5), and Philadelphia (15.8). All three sites set record snowfall amounts for the date and month. Combined with the record snow of 18-20 December 2009 records for the snowiest winters were set at these and other sites. After this storm, Washington had 55.9 inches breaking the record of 54.4 set back in 1898-99. Baltimore had a season total snowfall of 79.5 inches breaking the previous record of 62.5 set in the winter of 1995-96. Farther north, New York City (10 in) had a record snow event for the date. However, the Historic Mid-Atlantic Snow storm of 5-6 February 2010 did not impact New York City and thus only a daily record was set. This storm, similar to the previous two records storms of the winter of 2009-2010 occurred during a period of high latitude blocking and a period of low values of the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). Additionally, the winter of 2009-2010 was an El Ni�o year which is often characterized by an active southern stream while the negative phase of the AO and NAO often produce relatively cold conditions over eastern North America. Clearly, these events show the correlation between blocking, negative AO values and El Ni�o.

2010-02-06

The Historic Mid-Atlantic Snow storm of 5-6 February 2010. A strong storm moved across the Gulf of Mexico and up the East Coast of the United States on 5-6 February 2010 (Fig. 1). This storm produced heavy snowfall from Virginia to New Jersey. Many sites in Pennsylvania, Virginia, Maryland, Delaware, and New Jersey received record snowfall. Snowfall totals at some sites exceeded 30 inches in Maryland and Pennsylvania. Reports of snowfall in excess of 20 inches were common in the Pittsburgh, Harrisburg, Philadelphia, Washington, and Baltimore metropolitan areas.The storm total snowfall is shown in Figure 2. In terms of record snowfall, the snowfall in Pittsburgh, 21.1 inches, was a record for the date and the 4th all-time snowfall for the City behind the record storm of 24-26 November 1950 (27.4), 16-18 December 1890 (25.9), 12-14 March 1993 (25.3). At Washington, Dulles airport the 32.4 inches crushed the previous record set in January 1996. The 24.8 inches at Baltimore nudged out the old record of 24.4 inches set 16-17 February 2003 during the ?Presidents Day snow storm of 2003?. Philadelphia?s 28.5 inches was the second largest snowfall, second only to the 30.7 inches recorded on 7-8 January 1996. Finally, the 25.8 inches of snowfall at Wilmington, Delaware beat the old record set on 7-8 January 1996. Many locations set records for the date and the month. Harrisburg, PA set record for the date with 18 inches which as the 8th largest snowfall for the City. At this time the largest known snowfall was 38.3 inches in Maryland with 3.34 inches of liquid equivalent. This was the second major to historic snowstorm to impact the Mid-Atlantic region during the winter of 2009-2010. Double digit snowfalls are in a winter are relatively uncommon events in the Mid-Atlantic region. There are many aspects of this storm worthy of study. No doubt this will be a well studied event. Thus, our focus here is to document this event and show the value of anomalies in anticipating significant and potentially historic snow storms. Some NCEP forecasts are shown to demonstrate how well the models predicted the potential for heavy snow and how the models indicated a sharp area of uncertainty for the region where the heavy snow would rapidly diminish to light snow. GEFS GFS SREF heavy snow anomalies.

2010-01-30

A Pacific storm system moved across the southwestern United States, and then off the Mid-Atlantic coast producing a winter storm from New Mexico eastward to Delaware. A strong anticyclone to the north provided cold air and an enhanced baroclinic zone from Oklahoma to Maryland. To the south, the system produced heavy rains and along the northern edge the system produced snow. In the transition zone, freezing and ice pellets provide for a significant icing event from the Texas Panhandle, across Oklahoma and into Arkansas. Overall, the anticyclone and weak cyclone were relatively well predicted by the NCEP GEFS. The strong anticyclone in Figure 1 is a consistent feature found in many historic ices storms (Gyakum and Roebber 2001). In this instance, a strong anticyclone pushing low-level cold air similar to the pattern of several historic southern United States ice storms to include the northern Alabama ice storm of 1960 (Baker 1960). The strong LLJ (Fig. 6) south of the anticyclone was a good indicator for the regions receiving snow, freezing rain, and ice pellets. Stuart and Grumm (2006) noted the proximity of the anomalous LLJ and heavy snow in winter storms. The strong LLJ and anomalous easterly winds and the strong anticyclone were relatively well predicted by the NCEP GEFS (Figs 8, 9, 10). Thus a good synoptic signal was present supporting precipitation in the cold air. Tracking the 850 hPa low center (Figs 6, 9, & 10) clearly showed that the old Younkin rule (Younkin 1968) worked well for the snow associated with this event. Clearly the heavy snow was just a few degrees of latitude north of the 850 hPa low tracks, in close proximity to the most significant 850 hPa u-wind anomalies. This event was another good example of the value of easterly wind anomalies in defining areas of heavy precipitation and possible snowfall north of the 850 hPa low track. The sharp northern edge of the QPF was a problem. In the Louisville area, forecasts varied considerably. At times the GEFS suggested the potential for heavy snowfall and then backed off. Portions of the region, mainly south of the City itself saw heavy snow. Thus the uncertainty in tight gradient situations was considerable forecast issue.

2010-01-24

A strong storm moved across the United States from 21 January through 25 January 2010 (Fig. 1). This storm produced record rainfall and snowfall in the western United States from 20-22 January before moving eastward. As the storm approached the eastern United States on the 23rd and 24th of January it produced heavy rainfall in the eastern United States (Fig. 2) and 37 reports of severe weather in the southeastern United States. Most of the severe weather was on the 24th (Fig. 3). In the northeastern United States the key impact was heavy rainfall and minor flooding along rivers and streams. As the surface cyclone tracked into the Great Lakes (Fig. 1), a surge of unseasonably warm moist air moved into the eastern United States. This pattern indicated a Maddox Synoptic event type (Maddox 1979). Heavy rains were observed in the strong southerly flow with a widespread 25 to 50mm rainfall event over much of the Mid-Atlantic region and northeastern United States. In the Mid-Atlantic region, over 182 reporting stations reported over 50 mm of rainfall and over 30 stations received in excess of 75 mm of rainfall on over the two day period from 24-25 January 2010 (Table 1). This paper will provide an overview of the heavy rainfall event of 24-25 January 2010 in the eastern United States. The focus is on the patterns and the anomalies used to identify the pattern. Forecasts from the NCEP EFS are provided to show the value of using EFS probabilities and standardized anomalies to anticipate meteorologically and climatologically significant rain events.

2010-01-22

A strong Pacific jet brought a series of storms into the southwestern United States from 18-22 January 2010. The storm set several sea-level pressure records from the coast of California across Nevada and Arizona. These storms produced a wide range of high impact weather to include heavy rain (Fig. 2), heavy snow, severe convective storm (Fig. 3), and strong damaging winds. These storms impacts ranged from record low pressures set at sites in California and Nevada, heavy rainfall, record snowfall, widespread synoptic scale high winds, and severe weather. The severe weather included several tornadoes during the course of the event. This storm may likely replace the Columbus Day storm of October 1962 Storm (Lynott and Cramer 1966) as the most significant wind storm in the western United States. The Columbus Day storm still remains the ?Super Storm? in the Pacific Northwest. This high impact storm was relatively well predicted by the NCEP Global Forecast System (GFS) and the NCEP Global Ensemble Forecast System (GEFS). The forecast of 5 inches of rainfall over Arizona (Fig. 14). This forecast was in close proximity to where 5 to inches of observed precipitation. Anomalies...Ensembles...ranking events.

2010-01-11

The Big Chill of January 2010. During a period of high latitude blocking, the weather turned cold over most the eastern United States. The blocking actually impacted the weather across the northern hemisphere and cold weather and rare snows were observed in Western Europe and along the East Coast of Asia. During the period of cold weather the AO reached some of the lowest values in decades and the NAO was atypically low. The period of cold near the end of the blocking episode produced a prolonged cold snap over the eastern United States and produced snow over the Deep South. The snow in the Deep South accumulated in many locations from Louisiana to the coast of Georgia. Most of the snow fell between 6 and 8 January 2010. Snow and or unknown frozen precipitation were observed over the Florida Peninsula (Fig. 13). Many locations in South-central Florida had not seen snow or snow flurries since the cold episode of January 1977, another period where the AO and NAO were strongly negative. The negative AO pattern is often characterized by low pressure in mid-latitudes and relative higher pressure at higher latitudes. The sea-level pressure pattern and anomalies (Fig. 2c) show negative pressure anomalies over the mid-latitudes of the Atlantic north of 20N with the opposite sign (positive) over the Arctic. Thompson and Wallace (1998) looked for opposite pressure anomalies in the 37-45N region verse the anomalies over the arctic. In this case the negative phase is dominant. Hodges (2000) documented that in recent decades, the positive phase of the AO has dominated. They define the ?high index? as times where below normal Arctic SLP values dominate with strong westerlies in the north Atlantic which produce warmer and wetter conditions in Western Europe. The ?low index? which dominated from 15December 2009 through 10 January 2010 was associated with weaker westerlies across the Atlantic and thus colder and drier weather in Western Europe. From a forecast perspective, the negative AO was relatively well forecast. This is not surprising as there is relatively good skill in numerical models in predicting 500 hPa heights. In this case, the strongly negative AO and in previous events seems to suggest that cold events in the eastern United States are predictable in the 3-10 day range using the AO and its close proxy, the NAO, as a potential gauge for the event. The 500 hPa heights were relatively well predicted in this event (not shown) and thus AO values were also relatively well predicted. Another clue to cold episodes is the high latitude height anomalies (Fig. 1). When height anomalies are positive over a deep portion of the high latitudes, blocking is clearly evident and the NAO and AO should be negative or strongly negative.

2010-01-06

During a period of high latitude blocking a winter storm and unseasonably cold air impacted Western Europe. A polar low developed over southern England on 5-6 January 2010 and produced record snowfall over a large swath of southern England. Snowfall amounts in excess of 10 inches were both forecast and observed. This unusual snow and cold event occurred in a pattern with an unusually low AO and during a period of strong high latitude blocking. This may be an avenue of further research correlating cold and snow in Western Europe with low AO values and high latitude blocking. The 5700 m anticyclone over Greenland during this event is quite anomalous. The pattern over England during the snow was similar to those found over other parts of the northern hemisphere. The cold air at 850 hPa, the 850 hPa u-wind anomalies, and the location of the snowfall relative to the 850 hPa cyclone are features commonly associated with heavy snowfall in the eastern United States. Atypical in this case being the 850 hPa cyclone was moving to the west-southwest in this event. There appear to be many common characteristics to snow events through out the northern hemisphere. Clearly, numerical guidance provided useful clues as to the potential for an unusual event. The UKMO forecast (Fig. 1) suggests high situational awareness and good input to users of these forecasts. Knowledge of the pattern may also contribute to the success in forecasting this record event. Figure 14 (courtesy Medium-Range forecasting (ECMWF)) shows the snow depth over the British Isles. These data likely reveal good approximate total snow fall in southern England where 1 to 26 cm of snowfall is quite evident. The data over central England and Scotland likely represent accumulations over the entire cold episode and the snows of December 2009. Impressive features on this map include snow over Britain from Channel to northern Scotland and snow in northeastern Ireland. During this event, the heaviest snow was focused over southern England and the Reading area, in good agreement with the UKMO forecasts (Fig. 1). In addition to the snow, extremely cold temperatures impacted the region. This was a high impact winter event for much of Western Europe and the British Isle.

2010-01-03

An episode of high latitude blocking and a period of unusually low AO and NAO values allowed cold air to penetrate into eastern Asia. A cyclone developed along one of the frontal systems associated with a surge of cold air. This cyclone brought snow to eastern China and Korea. The snowfall over Seoul and Beijing represented record events at both locations. Though there was considerably more snow over Korea then eastern China. Seoul set a new record for the most snow since records began in 1937 and Beijing had its largest one day snowfall since 1951. The deep cyclone and strong easterly jet north of the surface and 850 hPa cyclones are a common pattern associated with heavy snow in the eastern United States (Stuart and Grumm 2006). There was a major winter storm in northeast China in March 2007 that also exhibited strong low-level u-wind anomalies (Grumm and Xuxuan). It would appear that there are some common signatures and some value in using anomalies to assess the potential for heavy snowfall in eastern China and Korea.

2010-01-01

An episode of high latitude blocking impacted the weather over North America and Europe during the month of December 2009. A series of deep cyclones over North America may have contributed to anomalous ridging over Greenland and northeastern North America. This high latitude blocking was associated with a strongly negative AO value, produced the lowest monthly mean AO for December since the records began in 1950. The negative AO was also associated with a negative sign in the NAO. The latter is often more highly correlated with the weather over North America, Europe and Asia. No attempt is made to explain why the high latitude blocks developed and how they relate to the NAO and AO. But based on previous record low AO events, high latitude blocking plays a significant role in the sign and magnitude of the AO. The high latitude blocking episode of December 2009 was associated with a pattern that produced highly negative AO values and negative NAO values. The average AO value for December 2009 was the lowest value ever recorded. Additionally, the value -5.67 on 21 December was one of the lower values recorded. A value of -6 would be one of the top ten lowest recorded AO events and was predicted to occur in early January 2010 by the NCEP GFS.