NATIONAL WEATHER SUMMARY
DECEMBER 2009
1st-5th
A
raging low pressure system located over the Southeast brought unsettling weather
activity to the southeastern quadrant of the nation on Wednesday. Rich and
abundant gulf moisture fueled the system and allowed it to drench much of the
Eastern Valleys, the Mid-Atlantic, and the Southeast with widespread rainfall
and areas of scattered thunderstorms. Increasing instability and strong dynamics
created a potential for severe thunderstorm development in the southern half of
Georgia and the Florida Panhandle. These severe storms are expected to be
accompanied by strong to damaging winds, isolated tornadoes, hail, and flooding.
Thus far, a tornado was reported this morning in Okaloosa, Florida, while areas
of localized flooding developed along areas of the Gulf Coast. Meanwhile, a
surge of cold air from the North continued to pour into the Central US today.
The cold airmass dampened afternoon temperature maximums significantly
throughout the region. Lowered temperatures supported a few pockets of snowfall
in the Dakotas. Quiet and chilly weather persisted elsewhere. Tranquil weather
conditions also developed in the West as high pressure continued to dominate
most of the region. Areas near the California coast started the day with gloomy
skies as dense fog lingered through the morning and into the afternoon.
Two
weather systems brought exceptionally wet weather to portions of the Gulf Coast
and Florida on Friday as low pressure developed in the Bay of Campeche and a
warm front lingered slowly over southern Florida. Florida saw the most
widespread wet weather, 90 percent of the state received at least some rain.
Thunderstorms were also noted across the state, but the most frequent lightning
occurred off the eastern coastline of the state.
This
front extended northeast from Florida up the Eastern Seaboard. While
precipitation stayed offshore in the East, clouds pushed back ashore, and made
for a cool gloomy day. In the western Gulf of Mexico, low pressure developed
rapidly on Friday morning as a trough in the jet stream dug into Texas. The
combination of the strengthening storm and the cold trough brought rain and even
snow to portions of Texas. In addition to the snow, the national weather service
issued a Freeze Warning for Friday night as temperatures were expected to drop
well below freezing, causing a hard freeze. In the West, High pressure continued
to be the dominant force for the region's weather. Cloud cover was mostly absent
throughout the region with the exception of some high clouds in the Rockies and
Northwest. Morning fog also rolled in across the West Coast, but had burnt back
by early morning.
The
first real shot of winter struck the Northeast on Saturday as a storm developed
off the Carolina coast and began to make its way north along the Eastern
Seaboard. Widespread snow was reported throughout the Appalachians in the
morning, with rain along the coast, but at temperatures fell throughout the day
many locations saw that rain change over to snow by the late afternoon.
Accumulating snow was mostly limited to grassy surfaces due to temperatures just
hovering around freezing. In higher elevation areas, such as northern New Jersey
and portions of Central Pennsylvania temperatures were much colder and moderate
snow accumulation was reported. To the north, in New England, temperatures were
warmer as winds off the relatively warm Atlantic Ocean transported heat ashore.
With the warmer weather came rain along the coast, with some wet snow in the
highest elevations. The winds were expected to switch around to the West
overnight dropping temperatures substantially. Cloud cover from the eastern
storm, tapered off west of the Appalachians, and clear skies were prominent over
the Plains. Some high clouds were noted streaming off the Rockies in the Western
Plains, but throughout the nation's mid-section Precipitation was mostly absent.
The Northern Rockies saw same light snow and some cloud cover. The West Coast
states stayed clear throughout the day on Saturday, with only a few clouds
overhead. Southern California saw a few areas of fog at the coast, mostly
limited to the beaches and a couple miles inland.
6th-12th
Wet
and wintry weather has fallen over most of the Rockies and started pushing into
the Plains on Monday. A strong low pressure system moved from the West Coast,
where it pulled abundant moisture in from the Pacific Ocean, and into the
Central and Southern Rockies. This system pushed a cold front through northern
California which brought scattered showers overnight with 0.18 inches of rain
reported in San Jose, California, while higher elevations saw a dusting of
snowfall. Winter weather advisories and blizzard warnings were issued for the
Great Basin and Central Rockies as this system intensified while moving over the
Rocky Mountains. Snowfall totals varied around 3 inches in Nevada and Utah,
while snowfall also initiated in Colorado with up to an inch of rain reported in
Denver, Colorado. Strong winds accompanied this system with gusts up to 23 mph
in Elko, Nevada. Wet weather also covered most of the East Coast on Monday. A
system in the Southeast picked up moisture from the Gulf of Mexico and spread
scattered showers over the South, with cloudy skies stretching into New England
and the East Coast. In Simpson, Louisiana, only 0.16 inches of rain was reported
on Monday. Most of the country remained cool with highs in the South in the 60s
while the North and Great Lakes region saw highs in the 30s.
An
intense winter weather storm hit the Central US on Tuesday as a strong low
pressure system stretched from the Rockies and into the Plains. Winter weather
and blizzard advisories have been issued from Colorado, over the Central Plains,
and into the Upper Midwest. Strong winds accompanied this system with gusts up
to 25 mph over Iowa and Nebraska. Most of the Northern and Central Plains saw
0.5 to 1 inch of new snowfall, while Des Moines, Iowa reported snowfall rates
ranging between 1-2 inches an hour. Cold and brisk conditions persisted over the
Central US with high temperatures in the 20s and 30s. This allowed for dangerous
road and travel conditions over most of the region. Snowfall diminished over the
Central and Southern Rockies on Tuesday as this system pushed eastward and out
of the region. A dusting of snow, and strong winds, lingered in some areas of
western Colorado. Extremely cold air poured in along the back side of this
system as highs only reached into the single digits with below zero wind chills.
In the East, the system pushed cloudy skies and cool temperatures into the
Northeast and New England, but snowfall has not yet been reported. Highs only
reached into the 30s on Tuesday. Out West, cold conditions persisted over the
West Coast as a strong low pressure system continued to spin in the Pacific.
This allowed for a cold front to drape over the region and allowed for highs to
remain in the 40s and 50s, while overnight lows dipped below freezing in most
places.
A
major winter storm produced active wintry weather from the Upper Mississippi
Valley through New England on Wednesday. Significant amounts of snow fell
throughout the Upper Great Lakes, while blustery winds of 20 to 30 mph and gusts
to 45 mph whipped across the region. This combination created periods of blowing
and drifting snow, as well as lowered visibilities. Whiteout conditions
developed in the open areas of Southeast Minnesota and northeast Iowa, as well
as the ridge tops along and east of the Mississippi River. Temperatures and wind
chill values across the region continued to fall during the afternoon, with wind
chill values falling to below zero values. In addition to this storm, dynamics
from an associated frontal system in the Mid-Atlantic and a weaker low pressure
system along the coast dumped moderate to heavy rain and snow with freezing fog
in the Northeast. Meanwhile, the southern half of this frontal system sparks
areas of light rain showers across southeastern Georgia and northern Florida.
Quieter weather conditions developed out West on Wednesday as high pressure
engulfed the region with cold and predominantly dry weather conditions through
the afternoon.
Areas
of active weather continued to pound the West, while the East received somewhat
of a break from wintry weather to end the workweek.
Another Pacific storm slammed into the West Coast, providing widespread rain and
high elevation snow through California and into the Great Basin. This
precipitation was only a prelude to the powerful storm that was expected to hit
the same area on Saturday. This storm will be even more intense with strong
winds, rain, and significant high elevation snow. This storm will be warmer than
the storm that brought cold, wintry weather to the area earlier in the week. A
thick layer of clouds shrouded the Gulf Coast, but only provided scattered rain
along the coast and in Florida. Rather, a high pressure system over the
Southeast provided widespread dry conditions for much of the East. One exception
to this dry weather occurred in western New York as lake effect snow developed
in the area. This snow developed due to cold air flowing over the relatively
warm Great Lakes. Dry, but chilly, conditions were experienced through much of
the rest of the country. The Northeast rose into the 10s and 20s, while the
Southeast saw temperatures in the 30s, 40s, and 50s. The Upper Midwest rose into
the 0s, 10s, and 20s, while the Rockies saw temperatures in the 20s and 30s. The
Northwest rose into the 20s and 30s.
13th-19th
Plenty
of active weather developed throughout he nation on Sunday. In the West, mostly
cloudy to overcast skies blanketed the northwestern quadrant of the nation as a
potent Pacific storm advanced from California and the Pacific Northwest to the
Central Rockies. Abundant moist flow poured into the region and interacted with
energy associated with this system to produce swaths of low elevation rain
showers and high elevation snowfall during the afternoon. Significant snowfall
throughout portions of the Intermountain West will aid in creating heavy snow
accumulations by the evening hours. The majority of the Intermountain West
remained under Winter Weather Advisories and/or a Winter Storm Warning.
Widespread clouds and areas of fog also covered much of the Eastern US on Sunday
while low pressure climbed up the Northeast coast and an associated front lined
the remainder of the East Coast. The system pulled a rich plume of gulf moisture
northward into the Great Lakes and the Northeast and produced light to moderate
rain showers from the Southeast through the Mid-Atlantic. A few embedded
thunderstorms accompanied rainfall in the Southeast. Meanwhile, a light to
moderate mix of wintry precipitation, with snow, sleet, and freezing rain, fell
across the Northeast.
The
Central US began the work-week with frigid temperatures on Monday as an Arctic
airmass moved into the region. Bitterly cold Arctic air from Canada plunged
southward behind an exiting frontal boundary over the Plains and dampened
daytime highs in the Central and Northern Plains. As the frontal boundary
dropped southward, high pressure filled in behind the disturbance and aided in
dampening daytime temperatures to well below seasonal averages. Meanwhile, a
wave of low pressure along the head of this frontal boundary advanced
northeastward into Upper Great Lakes by the afternoon. Energy associated with
this low combined with warm lake moisture to produce areas of light snow and
freezing fog in Wisconsin and Michigan. Elsewhere in the East, a frontal
boundary along the Gulf Coast continued to spark areas of light to moderate
showers, heavy rainfall, and thunderstorms in the Southeast, while high pressure
returned drier weather conditions to the Mid-Atlantic and much of the Northeast.
Quieter weather conditions developed throughout much of the West on Monday as a
wave of high pressure dominated weather activity through much of the afternoon.
Onshore flow along the coast increased as a large eastern Pacific storm advanced
closer to the Pacific Northwest and northern California shorelines.
Generally clear weather was reported across the nation on Thursday as two areas
of high pressure dominated the weather pattern. An exceptionally strong high
over the east helped usher in chilly temperatures to the region, with highs
generally hovering around freezing in the warmest parts of the Northeast, to the
low teens far to the north. Chilly weather even plunged into the Southeast where
temperatures didn\'t make it out of the 40s in many locations. In the West,
skies were clear throughout California, but some high clouds made their way into
the Northwest early in the day and rain followed suit along the coast.
Precipitation generally stayed to the west of the Coastal Range, but began to
sink southward into California by the end of the day. A few showers and snow
showers were reported throughout the western high plains, but no significant
accumulation was reported with these showers. The main weather event in the
country was a storm system in the Gulf of Mexico that brought continued heavy
precipitation to the Gulf Coast. Parts of Louisiana saw more rain on Thursday
and accumulated rainfall totals were up to 10 inches for this storm.
20th-26th
The
country saw mild weather on Monday, which gave a short break from wintry weather
conditions. A weak low pressure system hovered over the Great Lakes and brought
cool conditions to the region. With just a bit of moisture present near the
Great Lakes, the region saw light and scattered snowfall. Michigan and New York
saw less than an inch of total snowfall accumulation on Monday. Highs remained
in the 20s in most areas of the Northeast and Great Lakes regions. Meanwhile to
the south, high pressure build in over the Mid- and Lower Mississippi River
Valley and stretched eastward to the East Coast. This brought mostly sunny skies
and pleasant weather, but remained on the chilly side with highs in the mid-50s.
The Southern Plains also remained sunny and temperatures reached into the 60s.
However, the Northern and Central Plains saw increasingly cloudy skies as a
trough built in over the High Plains. This brought a threat for snow and wintry
weather, but precipitation has not yet initiated.
Further West, a low pressure system moved into the Pacific Northwest and
triggered scattered showers throughout the day with light sprinkles stretching
into Northern California. Seattle, Washington reported 0.40 inches of rain,
while snowfall in the Cascades ranged from 2-4 inches.
Widespread multi-level clouds spread from the Intermountain West through the
Plains on Wednesday as a large trough of low pressure reached back into Arizona
and spanned across the Four Corners, the Plains, and into the Upper Great Lakes.
Energy from this trough produced areas of significant and/or persistent mixed
precipitation throughout these regions and yielded to numerous Winter Weather
Advisories and Winter Storm Warnings. Another area of low pressure from Alberta
Canada, also known as an Alberta Clipper, dropped southward into the Central and
Northern Plains with a strong surge of cold air. Dynamics associated with this
system and it's accompanying cold airmass created areas of light snowfall and
freezing rain. The combination of these two aforementioned systems are forecast
to bring a major storm to the Great Lakes with more profound precipitation
through the upcoming holiday. Meanwhile, low pressure over the Central US will
drew significant moisture from the Gulf of Mexico across the Gulf Coast. This
high flux of moisture spread northward and produced areas of light to moderate
showers and heavy rainfall with thunderstorms through the Mississippi and
Eastern Valleys. Moisture also kicked up mixed precipitation in the eastern
portions of the Central and Southern Plains. Elsewhere, light snow fell across
Northern Maine as low pressure exited into the Atlantic Ocean. On the opposite
coast, mostly clear and quiet weather conditions persisted in the Pacific
Northwest and California as a ridge of high pressure remains the dominant
weather feature over these regions.
27th-31st
Wintry
weather moved into the Northeast on Monday. The low pressure system that brought
much snowfall to the Midwest over Christmas has made its way further over the
Great Lakes and into the Northeast and New England. This system has greatly
reduced in strength and size, but has brought scattered snowfall from the Ohio
River Valley up into Maine. Most areas saw snowfall accumulations between 1-3
inches. However, the eastern shores of the Great Lakes saw moist and heavy
lake-effect snowfall with accumulation up to 5 inches. Also, a winter storm
advisory has been issued over most of the Northeastern US as some areas saw
snowfall rates up to 1 inch per hour. This system continued to bring cool air
into the region with highs hovering around 20 in most areas. Behind this system,
with flow around the low pressure system in the East and high pressure that
built in over the Plains, cold air from Canada continued pouring into the
Central US. This brought dry and sunny conditions, but highs only reached into
the teens in the Northern Plains, while the Southern Plains remained near 40.
Out West, high pressure hovered over the Rockies and brought sunny skies and
cool temperatures. However, a low pressure system spinning off the West Coast
pushed ample moisture onshore and kicked up overcast skies and a few scattered
sprinkles over California and the Pacific Northwest. Highs remained in the 40s
and 50s over the region.
Jim G. Munley, jr.
http://www.jimmunleywx.com
