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
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.
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
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
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
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
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
This paper documents the event and shows some of the limitations of
numerical models and ensembles in predicting warm season heavy rainfall
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
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
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
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
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
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
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
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
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
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
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
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
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
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 -4850 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
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.