2009 Weather Case Studies for Central Pennsylvania

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2009-12-24 A major winter storm affected the central United States from 23-25 December 2009. The intrusion of cold air and a deep mid-tropospheric cyclone produced snow as far south as north Texas. This deep cyclone provided a rare white Christmas too much of the southern plains. The cost of this White Christmas included blizzard conditions on Christmas Eve. In the warm air, this strong storm produced heavy rainfall (Fig. 1), flooding, and severe weather (Fig. 2). Most of the heavy rain and severe weather was observed in north-south band in the region affected by the surge of high PW air and the anomalous LLJ southerly jet (Figs. 5& 6). Heavy snow was observed north and west of the surface cyclone and 850 hPa cyclone (Figs. 4 & 7). Most of the heavier snow fell in the strong low-level northeasterly jet north of the 850 hPa cyclone. The high latitude block, as shown in Figure 9 and the anomalous 500 hPa heights likely contributed to this unusual cut-off cyclone. The deep slow moving cyclone led to the cold air and precipitation remaining in place long enough for the cold air to change the rain to snow. Though not shown here, many locations in Oklahoma, Kansas and Missouri had rain, sleet and then snow. There are many interesting aspects to this storm which were not addressed here. The focus here was on providing an overview of an historic Winter Storm and the Southern Plains Christmas Eve Blizzard of 2009. Blizzard...Winter Storm...Christmas Eve
2009-12-19 An historic winter storm brought heavy snow and blizzard conditions to portions of the East Coast of the United States from 18-20 December 2009. Heavy snow was observed from North Carolina to New England. As the storm moved northward, it produced record snows and impacted the densely populated megalopolitan corridor from Richmond to New York City. Heavy and record snows fell over the major cities in this region. The 19th of December saw many new snowfall records set for cities from Washington to New York. Snowfall totals of 1 to 2 feet were quite common with most of the snow falling in the Mid-Atlantic region to southern New York on the 19th. The heavy snow lingered into the 20th over southeastern New York and eastern New England. The record snows in the New York City, Philadelphia, Washington and Baltimore regions are clearly related to nearly ideal condition including: ? The block over northeastern North America and the high pressure over eastern North America ? The surge of high PW air from the subtropics into the storm ? The anomalous LLJ aimed at the DC area.
2009-12-13 A retreating cold air mass produced ideal conditions for an ice event over central Pennsylvania on 13 December 2009. Due to strong warm advection, the event ended as light rain and drizzle and the temperature went above freezing over the entire affected region between 1800 and 2200 UTC. This case had a strong jet entrance region which likely helped maintain the low-level cold air. The warm air aloft was strong and there was little doubt that snow or ice pellets were a serious threat (Fig. 10 & 11). The 850 hPa temperatures were forecast to be above 0C (not shown) and verified close to observed (Fig. 4). The higher resolution NAM showed the extent of the low-level cold air better than the coarser GFS and SREF. In short term forecasting, higher resolution can play a very important role that our current global models and coarser ensembles cannot. The SREF indicated a potential, 40-80% chance for a brief period of freezing rain. This got forecasters thinking about the potential, but the finer resolution data in the NAM clearly out performed the other systems in its ability to simulate the low level cold air damming and the prolonged 4-7 hour period of freezing rainfall. There are times when the finer scale models will outperform the coarser global models and the coarser EFS?s. Forecasters need to be aware of this. In the near future, some uncertainty information will be obtained from finer resolution models by temporal and spatial adjustments. Thus the 0C contour in the NAM could be used to produce zones of uncertainty with respect to freezing rain. In the interim finer scale models advantages should be realized at shorter ranges leveraging their details and the probabilities from the ensembles. In this case, the fact that the SREF showed 40-80% chance of ice and that the finer resolution model showed strong cold air damming should have provide confidence in the colder solution of the higher resolution model. The courser GFS had no real chance at simulating the extent of the cold air damming.
2009-12-09 A strong jet and surface cyclone moved ashore along the West Coast of the United States on 6-7 December 2009. This system moved rapidly eastward producing significant weather from coast to coast. The ?transcontinental express? produced heavy snow in the mountains of the western United States; spread the coldest air of the season into the northwestern United States, and the plains; produced heavy snow from the southern plains into the Great Lakes; heavy snow from the Appalachians from West Pennsylvania to Maine; and severe weather and heavy rain in the Gulf States. The system left few places in the lower 48 untouched. The strong energy came under and block which had developed over western North America and the eastern Pacific. As the system moved onshore it pulled anomalously high PW air into the mountains of the western United States. This led to rain and mountain snows. As the system moved across the mountains it tapped warm moist air over the Gulf of Mexico and pulled it northward up the Mississippi Valley. The strong cyclone and the anticyclones to the north led to a strong low-level frontal circulation. A strong easterly jet with -3 to -4 SD u-wind anomalies developed in this region. Many areas affected by this LLJ saw heavy snow. The strong cold front, very warm and moist air produced severe weather along and ahead of the cold from Louisiana to South Carolina (Fig. 8). The surge of warm air led to the convection well to the north. Thunderstorms developed as far north as Pennsylvania and isolated severe weather was observed over western Pennsylvania and New Jersey. Thunderstorms were reported as far north as Massachusetts
2009-12-05 A weak surface cyclone moved up the East Coast on 5 December 2009. This system was associated with a strong north-south 250 hPa jet and had a strong easterly 850 hPa jet associated with it. The system produced 16 to 4 mm of rainfall along portions of the East Coast from North Carolina and Virginia eastward across Maryland, New Jersey, Long Island, and southern New England (Fig 3). The western edge of the precipitation shield was mainly snow with a good 2-7 inch snowfall event from Virginia into Maine. Some locally heavier amounts were observed. This was the first significant snowfall of the winter of 2009-2010 for many locations such as the Washington and Philadelphia metropolitan areas. This storm had some positive and negative aspects to it. The precipitation shield extended farther west and north than guidance initially indicated. Few forecasts ever got the north edge of the precipitation shield correct (Figs. 1 vs. Figs 13 &14). The NAM under predicted the heavy rainfall along the coastal plain. The overall synoptic pattern appeared to be relatively well predicted by the NAM, GFS, and SREF (no SREF features shown). But the edges of the precipitation shield were hard to predict. The 04/1400 UTC SREF QPF and POPS (Figure 15) suggest it offered little more information than the NAM or GFS. It did attempt to depict the band of heavier rainfall along the coastal plain. These data imply that there were considerable clues as to the potential for snow on the western edge of this system and for the heavy rainfall along the coast. The clues included the pattern, such as the strong jet and strong 850 hPa LLJ and u-wind anomalies. This case shows that there is considerable uncertainly, even at relatively short forecast intervals, in predicting QPF and the western edge of precipitation shields using NCEP models and ensembles
2009-12-03 A strong cyclone came out of the Gulf of Mexico on 2 December 2009. This storm system pulled up moist air which was connected to a region of very moist air over the tropical eastern Pacific Ocean (Fig. 4). The plume of moisture or the atmospheric river (AR), produced heavy rainfall from the eastern Gulf States into New England. The system also produced some severe weather (Fig. 1). The pattern associated with this event was a pattern quite commonly associated with heavy rainfall and severe weather in the eastern United States. The key features in such events include anomalous southerly winds, typified by a strong LLJ with strong v-wind anomalies and a surge of high PW air. Interesting to this event is that this plume of high PW was directly related to a potential source region. The PW plumes and the satellite data suggest this event had a tropical Pacific connection and is likely another AR case. The data shown here suggest that the pattern and the area of rainfall were relatively well predicted by the NCEP GFS, NAM, and SREF. Clearly there were details these models missed but the large scale area impacted and the surge of high PW air were shown to be well predicted by the NAM and GFS. This can be inferred in the SREF by its QPFs which suggested it too, by proxy, correctly predicted the pattern for heavy rainfall.
2009-11-30 An overview of the warm dry November of 2009. Focus on the Mid-Atlantic region and Pennsylvania. Anomalies and standardized anomalies are shown for the month of November. These data are compared to the anoamlies and pattern from 1 Sept to 30 November 2009. Key feature was the above normal heights and ridge over eastern North America. Key words: JRA Anomalies, November 2009.
2009-11-20 An atmospheric river brought a surge of high precipitable water (PW) air into Ireland and the United Kingdom on 18-20 November 2009 (Fig. 1). Preliminary reports suggest record rainfall was observed over Ireland, northwestern England and southwestern Scotland from 18-20 November 2009. The United Kingdom Meteorological Office (UKMO) indicated a storm on 13-14 November and 19-20 November impacted Britain. The focus here is on the event of 19-20 November. Initial reports suggest as much as 300 mm of rainfall may have fallen. The extreme heavy rainfall produced flooding in the Cumbria area of Britain. Similar atmospheric rivers (Ralph et al 2006 & 2005) have been observed along the West Coast of the United States. When these plumes of high PW air impinge upon land, interact with sloped frontal boundaries or interact with elevated terrain, they often produced heavy rainfall. The impact of moisture laden air and above normal PW standardized anomalies (Grumm and Hart 2001) into the West Coast of North America was documented by Junker et al (2008). They demonstrated the value of standardized anomalies of fields such as PW, winds, and moisture flux (MF) in defining areas where heavy rainfall would fall. Stuart and Grumm (2007) showed the value of standardized anomalies in defining and identifying heavy snow events in the eastern United States. Ensembles..PW...anomalies...Heavy rainfall
2009-11-12 The remnants of hurricane Ida came ashore on the 10th of November along the coast of Alabama and western Florida. The system tracked across Georgia and over the western Atlantic on the 11th through the 13th and then meandered to the east as it weakened. A strong area of high pressure and a larger scale ridge precluded the storm from moving to the north. The slow moving storm produced heavy rainfall from Alabama to the Mid-Atlantic region (Fig. 1). Some areas locally received 200-300 mm of rainfall as the storm lumbered up the coast. This event was realitively well predicted by the NCEP models and ensemble forecast systems.
2009-10-30 A relatively well known cool season heavy rainfall pattern set up over Mississippi 29-31 October 2009. This pattern produced a synoptic type heavy rainfall event (Maddox et al. 1979) across the region with some areas received over 4 inches (100 mm) of rainfall in about 24 hours. The timing and amount of rainfall support previous studies of heavy rainfall during the spring and fall in the lower Mississippi Valley (Korty 1980; Corfidi et al 1990, and Bellville and Stewart 1983). This event was well predicted and likely well anticipated by forecasters. The event was relatively well predicted by the NCEP NAM, GFS and by both NCEP EFS including both the SREF and GEFS. All systems forecast the pattern quite well relative to the verifying analysis from the GFS (shown). The QPF pattern produced by these systems clearly had the threat area well predicted, the rainfall amounts well predicted and thus all provided useful guidance and high confidence in a heavy rainfall event of a known type. This case is a classic example of how the patterns associated with heavy rainfall and the ensemble probabilities can be used to have confidence in a potentially significant rainfall event. The patterns can be viewed as the inside thinking or meteorology and the probabilities as the outside thinking or numerical values assigned to the event potential.
2009-10-15 A rare and historic early season snowfall impacted central Pennsylvania on 15-16 October 2009. At the official observation site at the Pennsylvania State University (PSU:STCP1) 4.7 inches of snow was recorded for the date. This broke the old record for the first snow and first inch of snowfall set on 17 October 1977. Officially, there have been 2 other snow events in State College in recent years including the events of 26 October 2005 and the 31 October 2002. It should be noted the STCP1 had 4.1 inches of snow on 1 November 1993, most of the snow fell on Halloween 31 October 1993 (Grumm and Nicosia 1996) fell on 30 and 31 October. The combination of heavy wet snow and leaves on the trees can make early season snow fall extremely destructive. So as with many early season snow events this record event was extremely destructive. When snow totals reached around 2 inches leaf burdened limbs and stressed branches began to snap and fall. As snow totals reached about 4 inches, large leaf burdened trees lost limbs and some fell over. It should be noted that most of the precipitation fell as snow and over 1.3 inches of liquid equivalent water fell during the event. Thus, the leaf and snow burdened trees produced power outages. It was estimated that about 27000 customers lost power between about 6 PM Thursday 15 October and 6 AM Friday 16 October. Around 12000 customers in State College lost power and Centre County accounted for a over 50% of the power issues .
2009-10-14 A deep cyclone affected the West Coast of the United States 13-14 October 2009. The storm produced heavy rainfall in the mountains of California and southern Oregon (Fig. 1). Over 128 mm of rainfall is shown in the coarse data displayed in Figure 1. Reports in California of locally heavy rainfall amounts over 250 mm (10 inches) and 300 mm (16 inches) were reported. In addition to the heavy rainfall, the storm produced strong winds in the mountains of California and western Nevada. Wind gusts of 30 to 50 mph were common throughout the region. In Nevada, higher winds with gusts over 75 mph were observed in a narrow corridor between I-80 and US-50. Over the Siera Crest, peak winds over 100 mph were common with a report of 135 mph near Lake Tahoe and Mammoth Lakes. The higher winds were mainly confined to the higher elevations of western Nevada and California. Snow also was observed mainly above 7000 ft. This strong storm had connection with Super Typhoon Melor. As the cyclone associated with Melor moved toward the Pacific Coast of the United States, it produced locally heavy rainfall from California northward to Oregon (Fig. 1). The storm had anomalously deep mean sea-level pressure anomalies (Fig. 2) comparable to the several historic storms from the past, including the historic 1962 ?Columbus Day? wind storm in the Pacific (Lynott, and Cramer, 1966). A recent ranking of historic Storms in the Pacific Northwest ranked the famous Columbus Day windstorm as the 10th strongest storm since 1948 (Graham and Grumm 2010). GEFS Ensemble anomalies
2009-10-09 Heavy rainfall affected the Missouri Valley on 9 October 2009. The heaviest rainfall was observed over Missouri and adjacent portions of Kansas, Arkansas, and Oklahoma (Fig. 1). The heaviest rainfall fell on the 8 October over the region shown in Figure 1. The large scale pattern was similar to the large scale patterns which have been identified to be associated with heavy rainfall over the Midwest (Junker et. al. 1999 and Junker and Schneider 1997). Key features (Fig. 2) included a strong jet entrance region just downstream of the affected region (Fig. 2b) and an approaching trough and jet exit region (Fig. 2a). This pattern implies a couplet jet circulation over the region. At 500 hPa there was a deep trough to the west (Fig. 2c) and a strong ridge to the south and east. Warm mid troposphere temperatures (Fig 2d) were present in the ridge. This note will document the heavy rainfall event of October 2009 over the Missouri Valley. The emphasis is on the pattern of this event relative to past events. The focus is on the ability of the NCEP models and ensemble forecast systems to predict the pattern and thus the potential for heavy rainfall. Ensembles Anomalies GFS NAM SREF heavy rainfall
2009-10-07 A deep cyclone moving through the Great Lakes and over southeastern Canada produced high winds across portions of the Mid-Atlantic Region and into southern New England. Wind damage was reported as far west as Michigan and eastward to the coast of New Jersey and New England. Over central Pennsylvania about 75000 people lost power due to trees down on wires. Reported wind values were generally in the 40 to 53 mph range, normally associated with a wind advisory category event. The event did produce significant impact to a wide range of people. A comparison of the pressure changes for the 12 February 2009 event (Fig. 8) revealed that pocket of 9 to 15 hPa pressure rises moved across Pennsylvania during that event compared to the 2-4 hPa/6hr-1 observed during this event. The French storm of 10 February 2009 showed 12 to 18 hPa rises with the wind event. The latter two events did produce more widespread damage and the French event produced massive power outages across northern France, a truly high impact event. Pressure rises... wind anomalies ... nonconvective winds
2009-09-22 A stalled east-west frontal boundary and a persistent area of low pressure produced a prolonged period of heavy rainfall in the southeastern United States from 19 to 22 September 2009. Rainfall amounts in excess of 12 inches were observed in the multi-sensor precipitation data (Fig. 1) and at observation locations in Georgia. The National Weather Service Office in Peachtree City, Georgia reported that ?the heavy rainfall caused significant runoff into area streams and rivers, resulting in major to record flooding across the Atlanta metropolitan area?. They indicated heavy rain fell on the 19th, 20th and 21st with 11.80 inches in Douglas County and as much as 9-12 inches reported in western sections of the Atlanta Metropolitan area. These rainfall amounts like are within the heavy rain area shown in Figure 1. The NAM provided poor QPFs relative to the GFS over the affected region.
2009-08-20 A weak frontal boundary sagged southward on 19 August 2008. The boundary stalled in southern Pennsylvania and remained in place on 20 August 2008. This boundary interacted with the warm moist unstable air along and ahead of it producing some severe weather, wind damage, in southeastern Pennsylvania (Fig. 1). A more widespread event is evident well to the west of Pennsylvania over Ohio where a stronger frontal system was progressing eastward. One of the storms that developed over eastern York and western Lancaster Counties produced wind damage and well photographed funnel cloud (Fig. 2). The picture was taken along route 322 in Lower Swatara Township in southern Dauphin County likely facing south into northern Lancaster County... This funnel cloud produced no reported damage.
2009-08-18 MCV line which produced severe weather with bowing segments over eastern Pennyslvania. A mesoscale short-wave moved across Ohio, West Virginia and Pennsylvania on 18 August 2009. The wave triggered showers and thunderstorms as it moved eastward. During the mid-afternoon hours, the line of showers and thunderstorms blossomed into a line of severe storms. These storms produced damaging and winds and a few reports of hail as it raced across eastern Pennsylvania into New Jersey (Fig. 1)
2009-07-30 July of 2009 will be remembered as a cool and wet month in the eastern United States and a bit hot and dusty in the western United States. Figure 1 shows the total monthly precipitation and the mean 500 hPa heights over the United States. These data show the wet conditions over southeastern New England, Florida, and portions of the Mississippi and Ohio Valleys. The 500 hPa height (Fig. 1) field showed a persistent trough over the eastern United States and a ridge over the western United States. Dry conditions dominated from Texas to the Pacific coast. It will be shown that below normal temperatures were present at lower levels near the trough axis.
2009-07-26 A well documented and recorded EF1 tornado which was mainly and EF0 tornado over most of its 1.25 to 1.50 mile long swath, affect Elk County from 1821 to about 1825 UTC on 26 July 2009. Clearly cell phone and digital technologies contributed to our knowledge about this event. The track in Figures 1 & 3 was derived from these images. The event clearly occurred in relatively weak large scale conditions and was not impressive on radar. After the fact it is clear that this storm was a weak, low topped supercell thunderstorm. Stronger storms have affected this region in the recent past with no impacts. Storms with rotation couplets in excess of 50 kts passed this region twice on 11 July and produce no reported damage. Why did this storm produce a tornado and those clearly stronger storms did not is an important question. Elk County Tornado
2009-07-23 Heavy rains fall over Pennsylvania and eastern New England on the 23rd of July 2009 (Fig.1) ahead of an upper level trough. The heavy rainfall over Rhode Island and Connecticut draw ones attention in Figure 1. Over Pennsylvania, the rain fell mainly in the late afternoon and evening hours from slow moving thunderstorms. The heaviest rainfall was observed in Cumberland and York Counties where reports of 5.7 inches were observed at Bloserville and Carlisle Springs and around 5.8 inches near Siddonburg. Heavy rains and flooding from 3 to 4 inches of rainfall was observed near and just west of State College, PA. The official COOP sites showed 4.10 inches in Cumberland County. The COOP data is heavily used in the UPD data shown in Figure 1. The key meteorological players in this event included a deep and unusually strong mid-tropospheric trough (Fig 1 & 7d), instability, above normal low-level moisture, and a trough moving across the region. Clearly, instability and upright convection played a role in the event over Pennsylvania. Though radar data was not presented, radar showed low-core and slow moving thunderstorms over the region. In New England, the event was better predicted and had stronger forcing and patterns more typically associated with heavy rainfall. This included the strong low-level easterly jet, the strong surface cyclone, and the above normal PW surge into the region. Despite the pattern being correct, the details in the heavy rainfall over New England were not well predicted. Figure 10 clearly showed significant variation in each successive 6-hour NAM forecast cycle. The shortest forecast, initialized at 23/1800 UTC may have been particular poor implying some model spin-up issues which caused an underestimation in the rainfall.
2009-07-11 An approaching cold front (Fig. 1b) and upper-level shortwave (Fig. 1a) produced severe weather across the northeastern United States during the afternoon and evening hours of 11 July 2009. The severe weather was focused over Pennsylvania and included a tornado over northeastern Pennsylvania (Fig. 1). In addition to the Pennsylvania, there was some severe weather over Missouri associated with a large MCS which developed on the flanks of a massive subtropical anticyclone and accompanying heat over the southwestern United States. The note will document the severe weather and tornadic event over Pennsylvania.
2009-07-01 June 2009 was unusually cool and wet over the northeastern United States. For cool weather, Boston had its 6th coldest June and many other locations in the Northeast were unusually cool. In terms of precipitation, most of the northeast and the Mid-Atlantic region were quite wet experiencing above normal rainfall and an unusually high number of days when rainfall was observed. So me locations had long stretches of rainfall and it rained over 50% of the 30 days of June including Boston, MA (22), Hartford, CT (24), Worcester, MA (22), Concord, NH (18), Portland, ME(21), New York City, NY (23), Poughkeepsie (17) and to the west, State College (16). An overview of the pattern for June and early July 2009 is presented here.
2009-06-26 An upper-level short-wave and cold front triggered convection over the Mid-Atlantic Region and northeastern United States on 26 June 2009 (Fig 1). The majority of the severe weather was in the form of hail (blue squares in Figure 1). There were some isolated wind reports in the northeastern United States, but removed from the upper-level trough wind reports dominated the severe weather over Tennessee and Kentucky and in the southeastern United States. This event shared many characteristics of eastern hail events, outside a favorable supercell environment. This event was dominated by steep mid-tropospheric lapse rates, a common feature in many eastern US hail events when the shear is relatively week. With a prolonged period with a deep trough over the eastern United States from mid-June to early July, there were several hail dominated severe weather events in the eastern United States. Dates of particular interest during this period included 15 June (all hail), 25 June, 26 June, 30 June, 1 July, and 7 July 2009.
2009-06-22 A large subtropical ridge brought warm dry conditions from eastern Texas to Alabama. Around this large subtropical ridge, a ring of moisture produced the classic "ring of fire". Along the edges of the ridge there were successive days of heavy rainfall and severe weather. Ring of Fire Subtropical ridge Severe weather heavy rainfall
2009-06-09 A weak shear day with high CAPE produced large updraft thunderstorms over the Mid-Atlantic region on 9 June 2009. The lack of shear precluded organization of most of the storms until later in the event. The large CAPE produced large cores. As shown in Figure 6, an interesting aspect of this event was the lack of shear. This suggested severe weather would be limited to big updraft storms due to the lack of shear. The CAPE and storm type was well anticipated. Despite the good forecasts and anticipating the event type. Warnings were difficult as storms popped up in the unstable air. Some were over sparsely populated areas and hail is poorly verified outside of populated regions. The -20C level was near 20KFT during the event. These storms typically pushed 50 dBZ cores to 30Kft and 60-65dBZ cores occasionally reached 25-30kft in the storms that produced the largest hail.
2009-06-09 A well predicted heavy rainfall event affected Botswana on 9 June 2009. Observations in Botswana indicated over 100 mm (4 inches) of rainfall in 24 hours. Estimated rainfall from the CMORPH and JMA are shown in Figures 1a&b. The CMORPH data showed upwards of 128 mm of rainfall while the JMA data indicated over 275 mm of rainfall. This event occurred with a common pattern observed in other heavy rainfall events found in other locations about the world. In this event, an anomalous 500 hPa cut-off cyclone with mid-level cold air combined with abnormally moist air to produce an ideal scenario for heavy rainfall. PW and u-wind anomalies, often found to be associated with heavy rainfall events, were on the order of 3 to 5 and -3 to -5 SDs respectively during this event. The anomalies clearly indicated a potential heavy rainfall event. The pattern associated with this event was well predicted and thus the NCEP GEF provided excellent guidance in predicting the pattern and the location for heavy rainfall. Using the concepts outlined by Junker et al. (2009) forecasters could have leveraged the large anomalies to better anticipate the heavy rainfall. It should be noted that the coarse global model predicted a high probability of 50 mm in 24 hours and 50 mm in 36 hours in Botswana (Figs 9-10).
2009-06-02 Warm episode over eastern Alaska. A well predicted warm episode affected Alaska on 1-4 June 2009. Temperatures in Juneau reached 80F on 3 June with a number of sites in the Alaskan Panhandle reaching temperatures well into the 80s. One remote observing site recorded a high temperature of 91F. Though the warmest temperatures were achieved on 3 June, most of the week of 1-5 June 2009 was very warm across most of southeastern Alaska. A well predicted warm episode affected eastern Alaska and the Yukon 2-6 June 2009. This warm episode shared the characteristics similar to previous events over the region to include the May 2009 warm episode (link). The large subtropical ridge, which was well predicted, produced all the tell-tale signals of a warm episode. This included the above normal 850 hPa temperatures west of the ridge axis and the surge of high PW air north and west of the subtropical ridge. The NCEP RMOP data showed that is was a well predicted and high confidence event. Clearly, several days out the NCEP data predicted the potential for a large and highly predictable ridge over Alaska and thus confidence in the above normal 850 hPa temperatures indicated by the NCEP GEFS RMOP GEFS anomalies....
2009-05-29 Heavy rainfall in southern and southeastern Pennsylvania. This was mainly a heavy rain event with above normal PW values and strong southerly winds. There were a few reports of severe weather.
2009-05-01 Alaskan warm episode with some record high temperatures. This well predicted event was readily found in the NCEP RMOP data as being highly predictable. Due to cold antecedent conditions, the onset of the warm temperatures produced snow melt. The warm air and influx of water caused ice in rivers to melt. Ice dams formed and did considerable damage to places like Eagele, Alaska, on the Yukon River. Anomalies and RMOP images showed the strong ridge and warm air associated with this event.
2009-04-27 An early season heat episode affected the eastern United States on 25-28 April 2009. This event was relatively well predicted at least 8 days in advance. This event actually began in the western United States and progressed eastward as the subtropical ridge moved eastward. The NCEP GEFS provided good guidance and high confidence in the eastern heat episode. Not attempt to quantify the western event was presented here. The GEFS clearly predicted the 500 hPa heights and anomalies associated with a strong subtropical ridge. Both the RMOP and standardized anomaly data aided in predicting and diagnosing this event.
2009-04-15 Well forecast rain event over the Mid-Atlantic region. Some banding and locally more heavy rainfall over areas of Pennsylvania. The event featured severe weather in the Ohio Valley and in the southeast. Well forecast by the GFS, NAM, and SREF.
2009-03-29 An early spring severe weather event affected the Mid-Atlantic region during the afternoon hours of Sunday, 29 March 2009. The system brought strong and damaging winds, large hail, and a tornado to the region (Fig. 1). The Storm Prediction Center images does not depict the EF1 tornado that touch down in Ephrata and Lititz, Pennsylvania around 440 PM on 29 March . The tornado was on the ground for approximately 1.25 miles with peak winds of 85-95mph and it caused 3 injuries. Large hail was reported over many portions of Pennsylvania eastward to New York. Dime size hail was reported as far east as Ridge, NY. Strong winds also were observed and damaging straight line winds were observed in York and Lancaster Counties causing damage to homes and trees.
2009-03-01 An ECWS brought heavy snow to portions of Tennessee, North Carolina, and up the East Coast of the United States to Maine. This was the first winter storm of the winter of 2008-2009 to bring widespread heavy snow to heavily populated corridor of the eastern United States. Snowfall totals of 6-10 inches were common from near the cities of Charlotte, NC, Richmond, VA, Washington, DC, Baltimore, MD, Philadelphia, PA, New York City, NY and Boston, MA. Some areas received 10-14 inches such as the Long Island, New York. The storm was a slow moving system and had a classic anomalous easterly low level jet which did relatively well outlining the region of heavy snowfall. Stuart and Grumm (2006) documented this association of the anomalous LLJ and heavy snowfall in ECWS. The storm also brought much need precipitation to the southeastern United States. GEFS..GFS..NAM..SNOW..ECWS..Anomalies.
2009-02-12 February Express the severe weather and synoptic high wind event of 10-12 February 2009. An intense cyclone zipped across the United States on 10-12 February 2009 producing widespread wind damage in its wake (Figure 1). The severe weather was observed from 10 to 12 February while the synoptic wind event was primarily on the 11 and 12th of February. This complex storm caused many areas to experience high winds associated with convection than, a few hours later, strong winds associated with a fast moving isallobaric high. In some locations, it was difficult to distinguish between the two events. Though each event was associated with distinctly different meteorological conditions. Narrow cold frontal rainbands and post frontal winds.
2009-02-11 A surge of warm air produced record high temperatures over much of Pennsylvania and the eastern Unites State on 11 February 2009 (Fig. 1). High temperatures range through the 50s and 60s over most of central Pennsylvania (Table 1) and most locations set new record highs for the day. It should be noted that NWS COOP sites record temperatures for the period of 7 AM to 7 AM and thus the high for 11 February is recorded on 12 February. The values for record highs are thus from 12 February data for all COOP sites. The event was well predicted by the NCEP global models and ensembles (GEFS) several days in advance. Well away from fronts and cyclones, the spread between members was relatively low and this event represented a high probability outcome event. None the less it represents a successful forecast. Due to the limits of predictability, all forecasts will show some degree of uncertainty and this event was no exception. The GFS and GEFS got the pattern correct with subtle difference verse the verifying analysis. Anomalies...record Highs...
2009-02-10 A deepening Atlantic cyclone moved over the English Channel on 10 February 2009. The storm brought strong non-convective high winds and rain to most of northern France. New accounts suggest hurricane force winds of up to 87 mph (140kph) affected northern and western France. The British Broadcast Company (BBC) report indicated that over 600,000 households across northern France lost power due to down lines and trees on power lines. Advanced forecasts of winds over 100 kph prompted the closing of Charles de Gaulle and Orly airports around Paris. High seas caused the cancellation of cross Channel Ferry services. As shown in the GFS and GEFS, the basic cyclone and strong winds were relatively well predicted at 1-2 day forecast ranges. This event shows the value of NWP and professional meteorologist in the decision support activities associated with significant high impact weather events. Ensemble probabilities of wind thresholds at 2 and 10m exceeding 50 and 70 kts would likely have been insightful though they were not produced here.
2009-02-04 During the evening hours, a mesoscale snow band set up over portions of Chester and Lancaster Counties. Radar suggests a similar, if not slightly weaker, snow band formed over portions of Adams and Cumberland counties. The snow began around 0000 UTC 4 February (7 PM) and the intensity picked up and after 0200 UTC (9 PM) snowfall rates of 3 inches an hour reported beneath this band. A video of this event was made at 2 AM of the 12 inch snowfall in Lancaster, Pennsylvania . The average snowfall in Manheim Township, Lancaster Pennsylvania suggested that 12 inches fell in 5 hours, a sustained rate of about 2.5 inches per hour. During the ?official? measurement it was claimed that this was ?a truly remarkable event? and thus the title of this document.
2009-02-03 A rare snow event struck Western Europe on 1-2 February 2009. This was reported, by newspapers and on the United Kingdom Meteorological Office (UKMO) to be largest snow fall over London and southern England in 18 years. The last event of this magnitude was observed on 7-9 February 1991. The snowfall was observed in the United Kingdom and in portions of France. New accounts implied that many business activities, schools, and transportation systems had to be close. New accounts reported ?transportation? nightmares as trains and tubes slowed or came to a halt. Snow being a relatively a rare phenomena, trains are not equipped to remove snow from the tracks. Additionally, with significant snowfall being so uncommon, snow removal equipment is normally not purchased or on hand to remove snow. The snow therefore was estimated to have cost about 1.3 billion British Pounds in losses due to the closing of so many business and government activities. The new report that the snow produced what was in essence a National snow day. The overall pattern was similar to the pattern observed during the snow event o 7-9 February 1991. These two snow events included a strong ridge at 500 hPa and surface anticyclone over Scandinavia and strong easterly flow. Each event included the passage of a strong cold front from the east with abnormally cold air behind the frontal boundary. Both events were characterized by strong low-level easterly flow and the evolution of an upper-level closed cyclone. Finally, in each event, a surface cyclone developed.
2009-02-03 Despite significant differences between forecasts from models from different modeling centers, inconsistencies in forecasts between successive runs of the same model, and considerable uncertainty in more traditional EPS data, a winter storm was grossly over forecast. The storm that verified was far weaker than advertised and was farther north and east of the location needed to have produced a significant event along the East Coast. It would appear that many forecasters did not examine or understand the uncertainty associated with this potential storm. This storm was not guaranteed to have a high impact on the eastern U.S. The data shown here, using simplistic ensemble techniques, suggests there was considerable uncertainty associated with the evolution of this storm. The true LAF from the GFS and GEM (Figs 2 & 9) quantified the differences. The large spread on the west side of the cyclone in all of the LAFs was due to the more eastward forecasts with time. Better methods of ensembling are available to forecast uncertainty; however these data illustrate how each modeling system is sensitive to small changes in initial conditions. Additionally, forecaster continue to monitor, compare, and bias their forecasts toward specific solutions. Thus, dProg/dt and LAF methods show how sensitive each modeling center models are to uncertainty in initial Megastorm, Groundhogvilla and other names followed this potential storm which never evolved close to its hyped potential.
2009-01-29 A heat wave struck southern Australia from 27 January to 02 February 2009. Clearly, the thermal anomalies show that the peak of the heat was from about 28-30 January 2009. The ridge clearly moved eastward and the thermal anomalies lessened after the 30th. The re-analysis data suggests that a 5880 m contour at 500 hPa is a good indicator of a subtropical ridge capable of producing record or near record heat. This is lower than the 5940 m contour often associated with heat waves over the United States. The re-analysis data clearly showed that subsidence near the ridge likely played a key role in the 2 to 3 SD thermal anomalies in the successive days from 27-31 January 2009. The low-level anomalies were quite close to the ridge. The 4 January 1976 data showed the same pattern and similar, though weaker ridge at 500 hPa. The data shown here imply the value in thermal anomalies and the subtropical ridge in diagnosing and forecasting heat episodes in Australia Temperatures were well above normal over the region and many reporting sites were 10 to 20C above normal. A record high of 41.5C was reported at Flinders Airport setting a new record high for Tasmania breaking the previous record of 40.8C set in Hobart on 4 January 1976. The 41.5C reading crushed the old record of 38.8C set in January 2003.
2009-01-28 Ice storm Arkansas and Kentucky. Mixed precipitation over Pennsylvania. A high impact ice storm struck the United States from Arkansas to Pennsylvania. Severe icing caused massive tree damage and power outages in many locations. News reports suggest Arkansas, Kentucky, and southern Ohio were particularly hit hard by this significant winter storm. Well over a million (1.3 million) customers lost power and perhaps 35 deaths were attributed to the ice storm. Due to the extensive damage to trees and power lines, many customers were informed that it could take over a week to restore power to hundreds of thousands of affected customers. The high impact of the storm was mainly felt on 27-28 January. Figure 1 shows the high resolution precipitation data in 6-hour increments from 0000-1800 UTC 27 January 2009. These data show that the precipitation arrived in Arkansas around 0000 UTC 27 January and then rapidly spread eastward into Illinois, Indiana, Kentucky and Tennessee. Details of the precipitation shield evolution are provided in section 3 of this document and the total accumulated precipitation in shown in Figure 2. This paper will document the ice storm of 27-28 January 2009. The goals include putting this event into a meteorological context relative to previously document ice storms and to show the value of ensembles in forecasting potentially devastating ice storms.
2009-01-24 A deep cyclone brought strong winds to portions of southern France, northern Spain and Italy on 24 January 2009. Tragically, the winds caused considerable damage and resulted in about 21 deaths. Most of the deaths were due to a roof collapsing near Barcelona, Spain. The deep Biscay cyclone, which tracked across southern France and into the eastern Mediterranean and into the Adriatic, brought the strong winds to the region. This cyclone appeared to be quite predictable by the NCEP GFS and GEFS. The both forecast the deep cyclone (shown only from the GFS) and the strong 850 hPa winds quite well. The wind probabilities suggested winds of 25ms-1 were a high probability outcome. The observed winds were considerably stronger than the forecasts. The east-west orientation of the Pyrenees Mountains may have played a role in the locally high winds in both southern France and northeastern Spain. Note the couplet of high winds (Fig.4b) north and south of the Pyrenees in southeastern France and northeastern Spain. Barcelona lies in close proximity to the v-wind maximum south of the mountains. The maximum in the GFS likely lies closer to Tarragona than Barcelona.
2009-01-23 South American heat wave of January 2009 compared to the pattern of the January 2003 heat episode. he pattern of sub-tropical South American heat waves was presented here. A comparison of the January 2003 and 2009 events was presented. Key features included an anomalous 500 hPa ridge and anomalous 850 hPa temperatures. It would appear a close 5880m contour at 500 hPa is a good tell-tale sign of a heat wave over subtropical South America. The data shown here suggests that this event was quite predictable and was well predicted by the NCEP GEFS. The probability fields of 2m temperatures suggest that 38C contour probability might be of considerable value for heat wave prediction in this region.
2009-01-17 An unusually strong surge of arctic air descended upon the United States, mainly east of the divide (Fig. 1), during the week of 12 January 2009. This air mass produced widespread sub-zero (F) readings across the United States from 13-17 January 2009. The coldest period was from the 15 to 18 January 2009 which is the period shown in Figure 1. The sub-zero readings in Pennsylvania represented some of the coldest reading in over 12 years and were likely the coldest readings, in many locations in the 21st century to date. The cold episode was relatively well forecast by the NCEP GEFS (Figs. 10-12) and other models (not shown). The guidance provided a long lead-time on the cold surge. The pattern associated with this event was quite similar to patterns observed in other cold Januarys from the past. The patterns at 700 hPa and 850 hPa for the 3 cold winters from 1977 to 1979 and the cold winter of 1994 were shown for comparison. They shared common characteristics to the event that unfolded in January of 2009.
2009-01-16 A surge of warm air into Alaska produced unseasonably warm weather over much of the State from 14-19 January 2009. Table 1 lists the temperatures and records for Anchorage from 8-20 January 2009. These data show that temperatures were below normal early in the month. Additionally, there was considerable snow cover over the State. The temperatures went above freezing on the 14th reaching a high of 37F. At the official observing site, temperatures remained above freezing until the 18th. Locally some areas went to freezing and the antecedent cold ground conditions produced severe ice problems on local roadways in and around Anchorage. A record high temperature of 50F was achieved on 16 January 2009. In addition to the warm daytime highs, several high overnight lows temperature records were achieved. Table 2 shows the temperature data for Fairbanks, Alaska. The onset of the warm temperatures was delayed a few days due to the more northerly latitude. The highest maximum temperature of 52F was achieved on the 16th. Similar to Anchorage, Fairbanks showed a complete reversal from cold to warm. An examination of previous days with record high temperatures and record high, high temperatures revealed certain common features. The more obvious feature was above normal 850 hPa temperatures during each event. Other features included a negative MSLP and 500 hPa height anomalies over the Aleutians and Bering Sea. Positive MSLP and 500 hPa anomalies were present over the western Canada. In most cases, above normal PW with +1 or greater anomalies were present over portions of Alaska.
2009-01-16 A surge of warm air into Alaska produced unseasonably warm weather over much of the State from 14-19 January 2009. Table 1 lists the temperatures and records for Anchorage from 8-20 January 2009. Tables 2 & 3 show temperature data for Juneau and Fairbanks respectively. These data show that temperatures were below normal early in the month. Additionally, there was considerable snow cover over the State. The temperatures went above freezing on the 14th reaching a high of 37F. At the official observing site, temperatures remained above freezing until the 18th. Locally some areas went to freezing and the antecedent cold ground conditions produced severe ice problems on local roadways in and around Anchorage. The RMOP images (Figs 9-11) showed just how predictable this event was. The large 500 hPa ridge, which was the dominant weather feature over the region, was highly predictable. The trough to the west, over the Aleutians was also relatively highly predictable. Thus, despite the lower predictability at 500 hPa over much of Alaska, the sensible weather was likely highly predictable. The key point is the RMOP shows the feature which is highly predictable. Thus the sensible weather between the relatively predictable Aleutian low and the very predictable ridge was likely more predictable than normal.
2009-01-10 A clipper brought snow from the Midwest to the East Coast on 9-11 January 2009. Snow fall totals generally were in the 3-7 inch range with this system, with some locally higher amounts in northern Illinois, southern Wisconsin, and Ohio where snowfall totals around 12 inches were observed in some isolated locations, to include Chicago. In Pennsylvania, the storm produced a widespread 3-7 inch snowfall over central and northern areas with some locally higher amounts in a few locations. The storm followed the generalized rules associated with winter storms and specifically Clipper events including: ? Snow fall with a Clipper generally requires that the cyclone pass to the south. ? Snowfall generally falls north and west of the 850 hPa cyclone, as in the ?Younkin rule? (Goree and Younkin 1966; Younkin, 1968; and Brown and Younkin 1970). This rule worked will in the Midwest with this event. The 850 hPa low actually tracked along the NY/PA border in the East. ? Regions along the track and south of the Clipper get little snow. In this case there was a strip of ice in Pennsylvania along and south of the track of the surface cyclone.
2009-01-07 The fourth significant ice storm of the winter of 2007-2008 affected the eastern United States on 6-7 January 2009. This storm produced ice, in the form of freezing rain and ice pellets, over much of central Pennsylvania. This event shared many of the characteristics common to recent ice storms, including an intrusion of cold dry air at low-levels before the precipitation arrived and a sharp east-west baroclinic zone. This was the fourth event in which the NCEP short-range ensemble forecast system (SREF) correctly identified the problem with regards to the precipitation type. The SREF clearly showed that freezing rain and ice pellets would be the dominant precipitation type. The few SREF members which forecast snow showed the snow was of short duration before a change over to mixed precipitation. Longer range forecasts indicated a slightly higher potential for rainfall. The event was generally well forecasts, in and of the fact that the longer range NCEP Global Ensemble Forecast System (GEFS) showed a high potential for a winter storm on our about 6-7 January 2009. Longer range forecasts ranged from a snow event, with the main cyclone tracking to the south to a nearly all rain event as forecasts began trending the storm track well to the north and west. The total liquid equivalent precipitation over Pennsylvania and the eastern United States is shown in Figure 1. Most of the precipitation over Pennsylvania fell between 2100 UTC 06 to 1500 UTC 07 January 2009 (Fig. 1a). This event was primarily a heavy rain event in the warm sector over the Ohio Valley and an ice event in from northern Maryland to southern New York State (Fig. 2). The heaviest rainfall was over the central Appalachian Mountains where over 100 mm of rain was observed in the mountains of western Tennessee. It will be shown that the higher amounts of precipitation were aligned with the PW and PW anomaly fields. Additionally, over Pennsylvania, the boundary between the warm air and low-level cold air focused the heavy precipitation over Pennsylvania (Fig. 1a).