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For: 2011 and Type: ALL these are the cases :

We have 34 events/cases to display for 2011 and Type: ALL


Abstract: . A record rain event, reported as one of the largest events in decades, brought flooding and landslides to the South Island. The heavier rainfall was confined to the northern and western side of the Island which was exposed to the strong northwesterly flow into the Island. A deep plume of above normal precipitable water moved into the Island from the north. The deep northwesterly flow about a strong mid-tropospheric ridge to the southeast and strong trough to the northwest brought the deep tropical moisture plume into the Island. Using re-analysis climate data (R-Climate) this event clearly illustrates the value of climate data to diagnose and predicted record and near record heavy rainfall events. Model climate (M-Climate) based forecast are presented to show the value of internal model climate data to aid in predicting extreme weather events. keywords: EFI R-Climate anomalies ensembles heavy rain


A deep cyclone raced across the northeastern Atlantic crossing northern Scottish Highlands and Eilean Siar between 1200 and 1800 UTC 8 December 2011. The cyclone central pressure was likely between 957-952 hPa as it crossed northern Scotland with pressure anomalies on the order of -3 below normal. A deep cyclone was present at 850 hPa and south of the 850 hPa cyclone center, southwesterly winds of 60-80 kts, which are 3 to 5 above normal, crossed northernmost Ireland and Scotland. The strong cyclone and 850 hPa winds produced damaging winds across portions of Northern Ireland and Scotland. New reports indicating there was damage to trees and power lines and the winds impacted ferry, rail, and air traffic across much of the region. Based on the United Kingdom Meteorological Office reports, Tulloch Bridge and Fair Isle registered wind gusts of 91 and 80 kts respectively. In the higher terrain of Scotland, Cairngorm Summit had a period from 1100 to 1600 UTC where wind gusts ranged from 102 to 143 kts peaking at 1400 UTC. The strong cyclone was well predicted by the NCEP, UK, and European Center models and ensemble forecast systems. The NCEP system showed the potential for an extreme event based on departures of these forecasts from climatology. The European Center Extreme Forecast index predicted the high probability of extreme winds at least 5 days prior to the onset of the winds. This papers focus is on the value of climatic data and model-climatic data to aid in diagnosing and predicting high impact weather events. Keywords: Ensembles standardized anomalies EFI high winds.


A mid-level short-wave moved out of the southern United States and up the west side of a strong ridge over the western Atlantic. The resulting strong southwesterly flow brought a plume of high precipitable air up the East Coasts resulting in heavy rainfall from the Carolinas in into New England. A large swath of the region saw 25 to 50 mm of rainfall with a few areas receiving over 75 mm of rainfall. Reagan National airport received 78.12 (3.1 inches) of rain on 7 December setting a new daily and monthly rainfall maximum. The rainfall resulted in mostly minor flooding in portions of Mid-Atlantic region where 16 points went over flood stage. All but 3 points experienced minor flooding. This was the first December flood event in the Mid-Atlantic region in 2011 and the eighteenth flood event of the calendar year. This fast moving rainfall event fell in a pattern often associated with heavy rainfall and was generally well predicted by the NCEP models and ensemble forecast system within about 48 hours prior to the onset of precipitation. Forecasts at 5-days out had the potential event but uncertainty issues arose and the events more persistent predictability horizon was limited to about 48 hours prior to the onset of precipitation. Like many winter events there was some snow on the northwestern edges of the precipitation shield. Key words: Rain flood ensembles uncertainty predictability SREF GEFS


A strong anticyclone moved over the Pacific Northwest beneath a large upper tropospheric ridge. Low pressure over the southwestern United States combined with this anticyclone to the north to produced strong easterly flow over the western United States. The resulting strong winds produced hundreds of reports of winds in excess of 50 mph and reports of wind damage. Wind gusts over 100 mph were reported near Mammoth Lakes, California (140 mph), Steamboat Spring, Colorado (123 mph) and Centerville, Utah (102 mph. The strong gradient between the large anticyclone and the weak low produced anomalous easterly flow. During the height of the event, low-level wind were 2 to 4 above normal during. These strong winds were predicted in the NCEP deterministic models and ensemble forecast systems several days in advance. This paper will document the event to include the pattern which produced this high impact high wind event. Forecasts from the NCEP SREF and experimental 16km SREF are used to address predictability issues associated with this event.


A fast moving mid-tropospheric trough brought a surge of moisture into the Mid-Atlantic region. The above normal moisture and strong low-level flow produced heavy rainfall in eastern Pennsylvania into southern New England. A broad area of in excess of 32 mm of rainfall covered most of Pennsylvania and New York. Portions of eastern Pennsylvania saw over 48 mm of rainfall as did an area of eastern New York and adjacent western Vermont. Locally heavier rainfall amounts, in excess of 64 mm were observed in portions of eastern Pennsylvania. The rainfall resulted in some minor flooding in portions of eastern Pennsylvania. The rainfall was generally well predicted.


A high impact early season winter storm impacted the eastern United States on 29-30 October 2011. The storm produced heavy snow from the central Appalachians northward across the Mid-Atlantic region into New England. Snowfall records for the month of October were set at many locations including 1.3 inches in Central Park in New York City to 32 inches in Peru, Massachusetts. A swath of over 6 inches of snow, with amounts well over 1 foot in many locations, was observed from central Pennsylvania into New England. This historic early season snow storm, with wet heavy snow combined with autumn leaves to produce widespread power outages. Reports indicated more numerous and enduring power outages in Connecticut were associated with this storm than tropical cyclone Irene back in August 2011. This relatively well predicted storm was associated with unusually cold air at 850 hPa, a surge of subtropical moisture on the warm side of the storm, and a strong low-level easterly jet. Strong easterly winds are common feature associated with most major and historic East Coast winter storms. Despite the base line climatology of little or no snow in October, numerical forecasts indicated a potential historic storm. Based on forecasts and the high probability of an historic event, forecasters were able successfully to predict with a high level of success the potential for an historic storm. Key words: Heavy snow record snow historic snow. East Coast Winter Storm. Anomalies and ensembles.


Abstract: A slow moving mid-tropospheric cut-off low brought a prolonged period of cool and wet weather to a significant portion of the eastern United States from 24-29 September 2011. A strong low-level easterly jet developed north of this feature and a strong low-level southerly jet developed to the east. The heaviest rainfall was observed east of the mid-tropospheric low in generally south-to-north aligned bands, in close proximity to the enhanced low-level southerly flow. They key features associated with this event included a large blocking high over the western Atlantic. This high was anchored by two massive troughs on its western and eastern flanks over the Pacific and Atlantic basins respectively. A plume of deep tropical moisture was present along the East Coast in the flow about western Atlantic subtropical ridge. Over the Mid-West the mid-tropospheric cut-off was the dominant feature. This cut-off low pulled a plume of high precipitable water air out of the Gulf of Mexico which produced heavy rainfall in the Ohio Valley before merging with the PW plume moving poleward about the western Atlantic subtropical ridge. These two moisture plumes likely contributed to the heavy rainfall and flooding in the Mid-Atlantic region on 27-29 September 2011. It is shown here that the National Centers for Environmental Predictions models and ensemble systems were able to predict the pattern and the persistence of this pattern. Despite the relatively good forecasts of the pattern, the systems had some difficulty predicting when the low would become progressive and they had difficulty predicting the location and higher end amounts of the rainfall. Key workds floods heavy rain cut-off low ensembles anomalies


Slow moving tropical storm Lee brought heavy rains to the Gulf States before lumbering up the Appalachians toward stalled frontal boundary. In the Mid-Atlantic region the initial rain was focused along stalled east-west frontal boundary. The axis of heavy rain was oriented in a west-southwest to east-northeast direction across central Pennsylvania. As Lee approached the region the orientation of the rain bands become more south-to-north, nearly orthogonal to the earlier rainfall axis. The data shown here imply that a 250 hPa Pacific jet and a strong short-wave with unseasonably cold air were critical in transporting the moisture associated with TS Lee up the East Coast which produced the synoptic type rain event on 7-8 September 2011. The rainfall event was the result of the convergence of several systems. This produced long duration frontal rain event over New York and Pennsylvania which transitioned to a synoptic event with periods of extremely heavy rainfall. The resulting multi-day rainfall event produced a broad area where in excess of 150 mm of rain was observed. Locally rainfall maximums in excess of 300 mm were reported by several observers. The north-south axis of heavy rainfall affected most of the Susquehanna Valley, this combined with heavy rainfall over portions of the same area from tropical storm Irene 8 days earlier produced near historic flooding at many points in the Susquehanna River Valley. As rivers rose the flooding began to compare to that produced by the remnants of hurricane Agnes in June 1972. From a forecast perspective, the pattern associated with heavy rainfall, to include 2 to 3 precipitable water anomalies and 3 to 4 low-level v-wind anomalies, were well predicted by the NCEP models and ensemble forecast systems. Heavy rain and the potential for near record rainfall was well predicted. Despite these useful forecasts, the models generally produced the heaviest rainfall 50 to 150 mm to far west of where it was observed. Anomalies Ensembles Flood Tropical Storm


Hurricane Irene brought heavy rains and flooding from the Carolinas to New England from 26-28 August 2011. The storm made landfall over North Carolina, New Jersey, and as tropical storm over New York City crossing central Park around 9 AM 28 August 2011. The tropical force winds extended well inland on the west side of the storm. As with many tropical storms, the heaviest rainfall was observed mainly along and west of the storm track. A 100-200 km swath of heavy rain was observed from the Carolinas to northern New England. Area averaged rainfall from gauge and radar data indicated a broad swath of 75 to 250 mm (3 to 10 inches) of rainfall. Individual rain gages showed locally heavy rainfall amount in excess of 325 mm (13 inches). It is shown herein that the forecasts of the heavy rain, to include the higher end amounts and the general location were well predicted by the NCEP models and ensemble forecasts systems. The surge of high precipitable water along a quasi-north south boundary in the coastal plain and strong winds was good signals for heavy rainfall. The models kept this feature close to where it set up and they did surprisingly well bringing the storm up along the coast. In the 2-4 day time frame the storm track was relatively well predicted.  


An unseasonably deep 500 hPa low moved over the eastern United States from 13-15 August 2011. This system triggered showers and thunderstorms which produced heavy rainfall along the East Coast. As it moved across the Midwest it triggered convection which led to the deadly tragedy at the Indiana State Fair. The deep low and the surge of moisture into the Mid-Atlantic region produced some locally heavy rainfall. Locally heavy rain from several bands of showers produced some impressive 24 hour rainfall totals. The highest totals were 10.64 and 9.20 inches in Seabrook and Bridgeton, New Jersey. This paper documents the event and shows some of the limitations of numerical models and ensembles in predicting warm season heavy rainfall events.


A persistent upper-level ridge brought a prolonged period of above normal temperatures to much of the United States and southern Canada. A broad mid-tropospheric ridge dominated the pattern the Great Basin to the East Coast. Cool air was limited to the Pacific Coast with a mean trough anchored over the northwestern United States and southwestern Canada. The heat wave peaked in mid-July over the plains. From 16-22 July 2011 a close 5940 m contour and +2 temperature anomalies dominated most of the central United States leading to record high temperatures and many new record high low temperatures. The ridge and associated warm air moved eastward. During the 3-day period of 21-23 July 2011 850 hPa and 700 hPa temperatures were +2 to +3 above normal. Record high temperatures were set or broken over much of the eastern United States during this time period. This paper will document the pattern and the anomalies in the pattern during the month of July 2011. The value of anomalies in diagnosing heat waves is employed here focusing on the period of peak heat from 16-23 July 2011.


Heavy rains impacted central Pennsylvania and the Mid-Atlantic region on 11-12 June 2011. The initial heavy rainfall early on 11 June created conditions conducive to flooding. The severe weather and heavy rainfall during the afternoon and evening hours of 11 June 2011 produced additional flash flood issues. The heavy rainfall was associated with generally week forcing but within a plume of high precipitiable water air. Strong warm advection was present during the event. The focus of this paper is on the pattern, how weak the flow was, and where and when the heavy rain fell. Short-term 12km NAM forecasts are presented to show how these data were of limited value in predicting the QPF associated with this event.


Severe event of 26 May 2011. Long-lived supercell storm moved out of Maryland into southern Pennsylvania. This storm produced a swath of wind and weak tornado damage. LCL heights were high at the onset of the event.


Three tornadoes affected central Pennsylvania on 23 May 2011. An EF2 in Juniata County, the Kellerville Tornado and the EF1 rated Winfield tornado are shown along with damage and survey maps of the paths of these two tornadoes. A short-lived EF1 tornado in Walker Township, Schuylkill County is also shown. Key words: Tornado survey supercell.


A series of tornadoes struck the central United States on Sunday 22 May 2011. Tornadoes were observed from Wisconsin southwestward into Oklahoma. An intense tornado struck the city of Joplin, Missouri resulting in over 90 fatalities. The Joplin tornado will likely rank as one of the deadliest tornadoes since the 9 June 1953 Worcester (94) and 8 June 1953 Flint tornadoes (116). The event of 22 May 2011 is the second deadly tornado outbreak of 2011 producing over 50 fatalities, coming just three weeks after the super outbreak of 25-28 April 2011 which resulted in 327 fatalities. The event of 22 May 2011 was associated with a moist unstable air with energy helicity index values over 5 in the southern Plains. Supercell thunderstorms developed and produced the tornadoes. Many of the standard parameters were well above levels often considered favorable for severe weather and tornadoes. Anomalies EHI RUC radar tornado


A slow moving 500 hPa cut-off low moving beneath a high latitude block produced a multi-day rain event over the eastern United States. Bands of rain and thunderstorms affected the region for over 4 days. During most of this time, the rain bands moved from southeast to northeast over the Mid-Atlantic region due to the deep easterly flow associated with the cut-off 500 hPa low. This case study emphasis is on the persistence of the pattern and the resulting weather. Composites of the pattern are presented using the global forecast system 00-hour forecasts. These data are compared to forecasts of the pattern from both the NCEP global forecast system and global ensemble forecast system. Knowledge of persistence and high confidence in persistence may be of value in identifying periods of heavy rain. Key words anomalies persistence GFS GEFS cutoff


An historic and tragically deadly tornado event struck the eastern United States on 27-28 April 2011. This was comparable to the deadly 3-4 April 1974 and 18 March 1925 events which caused over 300 and 740 deaths respectively. The expansive event of April 1974 affected 11 States and was associated with large low-level wind anomalies and an unseasonably strong upper-level jet stream. The 850 hPa low-level jet peaked at over +4.5s above normal on 27 April 2011, accompanied by precipitable water anomalies in excess of +2s above normal. The 250 hPa jet core was over 3s above normal, over the Great Lakes with a broad implied jet entrance region of the southern United States. This anomalous pattern is shown using the GFS 00-hour forecasts. Forecasts from the NCEP models are used to show how predictable this pattern was. Clearly, National Weather Service’s forecasters used these data and this and additional information to anticipate this historic event. Undoubtedly, anticipating this event and communicating this event to the public by the broader weather community reduced the loss of life. Despite the successful forecasts and communication of this information, this event will go down as one of the deadliest tornado events in United States history. Keywords: Severe tornado, anomalies, ensembles.


A persistent pattern produced a multi-day rain event which resulted in devastating flooding over portions of the Mid-Mississippi Valley in April 2011. Successive heavy rains, or meteorological events from 19-26 April 2011 produced a high impact hydrological event over the region. Each rainfall event was meteorologically significant but the collective impact of the persistent pattern played a critical role in the historic flooding which followed. Composites of the pattern indicated that in the mean, a plume of high precipitable water air, a strong low-level jet, and a persistent jet entrance region remained over the region for over 7 days. Each meteorological event impacted slightly different regions. Successive rainfall events over a relatively similar geographic area were a contributing factor to the severity and impact of this long duration hydrologic event. Standardized anomalies are often used to determine the meteorological and climatological rarity of a weather event. Applying this concept to patterns over periods of 1 to 10 days may help understand some of the historically significant events. Applying this concept to numerical output and ensemble output may aid in predicting these historically significant events. This concept is applied here to the Mid-Mississippi Valley floods of April 2011.


A developing early spring storm system brought widespread severe weather from northeastern Texas to the East Coast on 19-20 April 2011 (Fig. 1). With over 890 reports of severe weather (Table 1) on 19 April, this was the second largest total since 2005. Only the massive event of 4 April 2011 produced more events with over 1476 severe reports. Both cases were associated with high moisture flux and both events had record report amounts.


A developing storm system brought severe weather, with over 1000 reports of severe weather and 267 tornadoes, from the southern plains to the Carolinas over a 3 day period spanning 14-16 April 2011. The tornado outbreak in North and South Carolina was likely the largest and most significant tornado outbreak since the 28 March 1984 event which included 22 tornadoes which killed 57 people. The rain and severe weather were closely linked to the surge of high precipitable water and strong southerly flow ahead of the advancing frontal system. Thus, high moisture flux values, with anomalies on the order of 4 to 6 were common during the event and were often found in close proximity to the areas of heavy rainfall and severe weather. The latter areas were also associated with high values of convective available potential energy. The surge of dry air, with low values of precipitable water clearly played a role in the convection and tornadoes of both 14 and 15 April 2011. The precipitable water anomalies in the southern plains into the Gulf States was -1 just behind the cold frontal boundary. There may value in using PW anomalies to gain insights into the character of dry lines and their potential to produce severe weather. In this event, similar to 10 May 2010, a surge of abnormally dry air was present during much of the event.


A strong upper-level wave and jet stream pulled shallow moist air northward into the plains States and an elevated mixed layer over this warm moist air mass. This early season elevated mixed layer combined with strong winds to produce what can only be described as a massive severe weather event. With over 1200 reports of severe weather, mainly from strong winds, this was likely the largest and most extensive severe weather event over observed over the United States. With over 1200 reports of severe weather this event eclipsed the events of 2 April 2006 (872) and 7 April 2006 (871) which were the previous top 2 events since 2005. Only 12 events since 2005 have produced 500 or more severe weather reports. Whether this event was truly historic or represents a reporting bias is not clear. The strong upper-level jet, strong low-level jet, and high values of precipitable water combined with an elevated mixed layer clearly combined to produce a meteorologically and climatologically significant severe weather event. Most fields associated with severe weather, such as low-level winds and precipitable water were 2 to 4 above normal during the event. Other fields such as moisture flux were extremely anomalous on both 3 and 4 April 2011.


A complex early spring storm brought snow, sleet, freezing rain, severe weather, and a confirmed tornado to Pennsylvania on 23 March 2011. Most of the snow fell across north-central and northeastern areas of the State with some sleet into central and south central areas of the State. As the cold front approached, severe weather developed in the surge of warm air. Temperatures soared into the 70s in southwestern-most Pennsylvania. The low-level cold air held fast in most of central and northeastern portions of the State. Standardized anomalies and ensembles.


A slow moving north-south oriented frontal band brought heavy rainfall to the Mid-Atlantic region on 10-11 March 2011. Rainfall exceeded 75 mm over a broad region of eastern Pennsylvania, New Jersey and southern New York State. Coming on the heels the heavy rainfall event of 5-6 March 2011, flooding was observed over most of the same region. Many points in eastern Pennsylvania saw moderate to major flooding. Northern New Jersey saw several points reach the 3rd or 4th highest flood stages on record. This was a classic Maddox-Synoptic type event, with sharp north-south frontal system. The precipitable water and wind anomalies ahead of the frontal boundary were 3 to 4 above normal. The 850 hPa moisture flux was typically in the 3 to 4 range during most of the event. The hourly 13km RUC data showed surges of moisture flux anomalies around 6 during the periods of heavier rainfall. The large scale pattern was relatively well predicted 3-5 days in advance of this event. However, the NCEP GEFS predicted the heaviest rain to fall over extreme eastern Pennsylvania and the SREF predicted most of the heavy rainfall to fall over eastern Pennsylvania. The SREF under forecast the heavy rainfall over southern New York and hard-hit areas of northwestern New Jersey. When used in tandem, the GEFS and SREF produced a reasonable forecast of the overall area impacted by the heavy rainfall.


A slowly retreating anticyclone over the western Atlantic and an approaching anticyclone moving out of western Canada produced a multi-faceted precipitation event over the eastern United States on 5-7 March 2011. A deep moisture plume from the Gulf moved up the Mississippi and Ohio Valleys producing a large area of heavy rainfall. Cold air from the advancing anticyclone turned the western edge of the precipitation to snow. Heavy snow developed on the western side of the frontal zone as a wave developed along the frontal zone. As this wave moved up the front, heavy snow was observed from south-central Pennsylvania into New England. The 25.8 inches of snowfall in Burlington, Vermont was the 5th largest snowfall on record and the largest record snowfall for the month of March. Many locations in northern New York and New England received heavy snow with reports of 24 to 30 inches in several locations. In the warm air, the strong southerly flow and deep moisture produced heavy rain. The rainfall combined with snow melt produced flooding across Pennsylvania, New Jersey, New York and southern New England. Major flooding was reported in New Jersey. Forecasts for the heavy rainfall were relatively good. However, the rapid change over from rain to snow and the rapid snow accumulations were generally under predicted. The value of high resolution in near-term forecasting, despite relatively poor forecasts at longer ranges is presented here to show the value of these data a extremely short-ranges.


A high impact late winter storm brought severe weather, heavy rain, and snow to much of the United States east of the Rocky Mountains. Over the course of two days there were over 356 reports of severe weather from Kansas to Maryland. There were several tornadoes and numerous reports of large hail, which is not a typical severe weather observation in February. The event was associated with a strong storm system which moved through the region. Strong low-level winds and a surge of high precipitable water air contributed to the shear and instability which produced the severe weather and the heavy rainfall. This was the largest severe event to date during the winter of 2011, coming on the heels of the event of 25 February 2011. Like many La Niña winter severe events, it was associated with a modest surface cyclone, above normal precipitable water, a strong low-level jet and above normal low-level moisture flux.


A high impact late winter storm brought something for just about everyone. Heavy snow fell along the northern edges of the storm in the low-level easterly jet. Heavy rain fell near the warm frontal boundary and in the warm air moist air over the central Mississippi and Ohio Valleys. The heaviest rainfall was over the Ohio Valley where the NCEP SREF predicted the highest probability of heavy rainfall. Severe weather occurred in a north-south band along and ahead of the cold front. The severe weather was associated with a plume of above normal southerly 850 hPa winds, above normal precipitable water, and above normal moisture flux. With over 284 reports of severe weather this was in impressive severe event for late February. For good measure, there was a minor ice event in the cold air over Pennsylvania and a brief period of synoptic scale high winds behind the cold front.


Two waves moving along a frontal boundary on 20 and 21 February 2011 brought heavy snow from Minnesota to Pennsylvania. The first band heavy produced snow farther than the second band. Along the southern flank of the first snow band, there was an area of freezing rain and ice pellets. The second wave tracked farther south bringing mostly rain to the Ohio Valley and snow during the evening hours of 21 February to western Pennsylvania. In Pennsylvania heavy snow fell about 100 to 200 km farther south with the second wave. The snow in both waves was well aligned with the easterly low-level jet in the cold air. The heaviest snow fell in areas where the easterly wind anomalies were general -2 to -3 below normal. The NCEP short-range ensemble forecast system (SREF) short-term forecasts provided excellent guidance as to the high probability threat areas for heavy snow and ice accumulations. No explanation for the high predictability is offered here. However, these data likely contributed to well crafted winter storm warnings and advisories which depicted the sharp gradients forecast by the SREF and other NCEP numerical guidance.


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


A major winter storm impacted the United States from the southern plains into New England from 31 January through 2 February 2011. North and west of the storm track, from Oklahoma to Michigan, heavy snow was observed. Many locations received record or near record snowfall. Chicago had 20.5 inches of snow which made this storm the 3rd largest snow event in windy city. In the warm sector, rain and severe thunderstorms impacted areas from Texas to Georgia. Most of the severe weather was in Texas and Louisiana. Farther east, shallow cold air produced an ice storm over portions of Pennsylvania, New York and New Jersey. The heavy snow fall was in close proximity to an anomalous low-level easterly jet. Near the regions where 15 to 22 inches of snow were observed, the 850 hPa u-wind anomalies reached -5s below normal. The strong winds were the result of a strong anticyclone to the north and west; and a deepening surface cyclone. The cyclone phase of the snow event showed a classic jet coupled jet signature over the Midwest. Forecasts of this complex and far reaching storm suggest that the storm was relatively well predicted by the NCEP operational models and ensemble forecast systems.


Tropical storm Yasi crossed the Coral Sea and made landfall in Queensland Australia as a category 5 tropical storm. Despite heavy rainfall, winds over 100 KTS and a 5m storm surge, the storm caused no serious injuries. Damage to buildings and crops were significant. This storm was associated with a surge of high PW air which may be associated with one of the largest PW values recorded in recent memory. This clearly was a significant, high impact tropical cyclone. The 80 to 85 mm PW values at 02/0000 and 02/0600 UTC may be an artifact of the GFS analysis. Numbers will be derived from the NCEP/NCAR re-analysis for comparison when they become available. The numbers from the re-analysis data will likely be somewhat lower. From an anomalies perspective, this storm was associated with some extreme values of anomalies. It is rare to have several variable meet or exceed 5 but during this storm there were many variables which reached 6 anomalies. This suggests this was an extremely high impact and relatively rare storm.


A high impact winter storm impacted the eastern United States on 26-27 January 2011. The storm brought heavy snow from the Washington, DC metropolitan area northward to Boston. All of the major cities in this densely populated corridor received heavy snow. The snow restricted travel over the entire region clogging roads and causing the cancelation of hundreds of flights. Most of the heavy snow fell in a brief period lasting 3-6 hours in most locations. Despite the short-duration, snowfall amounts of 8 to 20 inches were common in the corridor from Washington, DC to Boston, Massachusetts. The 19 inches in Central Park, New York contributed to the record snow for the month making January 2011 the snowiest January on record for New York City. The intense snow bands were aligned with -3 to -4850 hPa u-wind anomalies. This was another example of the value of anomalies in identifying winter storms which can produce meteorologically and climatologically significant events. From a forecast perspective, the storm posed considerable forecast problems. Early forecasts implied that the storm would occur on 25-26 January 201l. These forecast proved to be too fast. A northern stream wave brought some light snow to the region early on 25 January. However, the main system in the southern stream was about 24 hours slower than earlier forecasts. Shorter range forecasts handled the main southern stream system quite well, though most forecasts missed the predecessor snow and rain which moved through the affected region 8-14 hours prior to the main event. key words: ensembles anomalies snow snowbands


A high impact winter storm brought heavy snow from eastern Pennsylvania into New England on 11 to 12 January 2011. The heaviest snowfall between 15 and 31 inches fell over Long Island, New York, Connecticut, Rhode Island, southern Vermont, New Hampshire, eastern New York and Massachusetts (Fig. 1). Snowfall amounts over 20 inches were focused in Connecticut and western Massachusetts (Fig. 2). This was the second high impact East Coast Winter Storm (ECWS) to impact the New York byte and southern New England in two weeks. Unlike the previous storm, this storm was relatively better predicted by numerical models and ensemble forecast systems (EFS). The primary wave came out of the southern stream (Fig. 3) producing snow and freezing rain across the southern United States from Texas to the Carolina’s. The southern stream wave merged with another stream wave which was over the Midwest by 1200 UTC 11 January 2011 (Fig. 3e). As the two systems merged, a period of rapid cyclogenesis was observed along the East Coast (Figs. 3f-h). The cyclogenesis occurred too far north, sparing the Washington DC metropolitan region significant snowfall. West of the storm an area of high pressure with above normal surface pressure dominated the region. Along with this strong anticyclone there was unseasonably cold air. It will be shown that this storm shared the characteristics often associated with meteorologically and climatologically significant ECWS. The key features (Stuart and Grumm (2006) include a deep cyclone and anomalous easterly winds north of the surface cyclone. The historically significant storms typically have -3 to -5 u-wind anomalies. In this storm -5 u-wind anomalies were observed. The value of standardized anomalies in identifying high impact significant weather events has been demonstrated by Graham and Grumm (2010), Grumm and Hart (2001) and Hart and Grumm (2000). The forecast applications apply to winter storms and heavy precipitation events (Junker et. al 2008;2009) and excessive heat events (Grumm 2011). This note will document the ECWS of 11-12 January 2011. The focus is on the pattern and anomalies associated with the storm. The value of EFS and anomalies with EFS data are presented.


The southern ice storm of 9-11 January 2011 was a result of a low pressure center moving along the northern Gulf of Mexico interacting with a strong surface high to the northeast. A strong cold front draped to the south of the Low was associated with severe weather in southeast Texas. High pressure, centered over the Ohio Valley, had settled in ahead of the storm provided surface easterly flow which held cold air in place. Warm moist air over the Gulf of Mexico was displaced northward by a strong low level jet over the cold surface air to create significant ice accumulations. The weather pattern associated with this event had many of the common aspects of an ice storm as outlined by Grumm et al 2007. This paper will identify the key aspects and the larger scale pattern associated with this storm.


Surges of tropical moisture and strong low-level flow produced locally heavy rainfall over southern Queensland on 8-11 January 2011. Heavy rainfall atop of wet soils and receding flood waters produced devastating flash flooding. Flood water rushed through the city of Toowommba, west of Brisbane. Several deaths were reported and 70 people were missing. The rain fell on an already saturated region where enhanced rains associated with La Nina were setting records. This more recent event showed that heavy rains were closely associated with surges of 3 to 6 moisture flux anomalies and surges of 2 to 3 precipitable water and -4 to -5 850 hPa u-wind anomalies. The forecast data shown here implies that the deterministic global models predicted heavy rainfall over southern Queensland during the period of heavy rain and flooding. It appeared that the NCEP GFS was producing an internal model maximum 24-hour QPF during the event which appeared to be between 128 and 160 mm. Over the time of flooding several GFS forecast cycles produced over 300 mm of QPF which was within 85% of observed values. This implies a remarkably predictable pattern capable of producing historic rainfall amounts. The standardized anomalies of key fields suggest that the pattern which produced the heavy rainfall and flooding implying a meteorologically and climatologically significant events. Low-level wind anomalies were over 4 above normal, precipitable water anomalies were 3 and moisture flux anomalies near the period of heaviest rainfall on 10 January 2011 were over 6 above normal.