weather

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Tue Dec 17 2024
Valid 12Z Tue Dec 17 2024 – 12Z Thu Dec 19 2024

…Another Atmospheric River to bring heavy coastal rains and high
elevation mountain snow to the Northwest…

…Unsettled, wet weather expected for most of the eastern U.S.
Wednesday…

…Periods of snow for the Northern Plains through mid-week with heavier
accumulations most likely Wednesday night…

…Much above average temperatures expected for most of the lower 48 into
mid-week…

Yet another Pacific system will help to usher in a wave of Pacific
moisture/Atmospheric River into the Pacific Northwest and inland over the
northern Great Basin/Rockies Tuesday. A more northerly track will help to
focus the heaviest lower elevation rainfall along the coastal ranges of
northern Oregon and Washington State, with heavy high elevation mountain
snow for the northern Cascades. Some moderate snow accumulations will also
be possible into the northern Great Basin and northern/central Rockies,
aided in part by a leading wave departing the region early this morning.
Lower elevation inland locations can expect a wintry mix of rain and snow,
with some freezing rain possible to the east of the Cascades in
Washington. Precipitation chances should come down through the day
Wednesday for the Pacific Northwest while lingering longer in the northern
Rockies.

A lingering frontal boundary will help to trigger some showers and
thunderstorms over portions of the Southern Plains east into the Lower
Mississippi, Tennessee, and Ohio Valleys through the day Tuesday. An
approaching upper-level wave will help to reinforce the boundary overnight
Tuesday and enhance moist, southerly flow from the Gulf, leading to
increasing storm coverage and locally heavy rainfall. The boundary will
push eastward as a cold front towards the East Coast through the day
Wednesday spreading showers and storms into the Southeast and coastal
Northeast. Colder air in place to the north over the interior Northeast
will lead to snow showers with some light to moderate accumulations for
higher mountain elevations.

A quick moving upper-level wave will bring some snow showers to portions
of the Northern Plains/Upper Midwest today with some light accumulations
possible, especially from central South Dakota east through southern
Minnesota. These light snow showers will spread eastward into the Great
Lakes Wednesday. Then, another more potent wave will approach from the
west during the day Wednesday leading to lee cyclogenesis over the
northern High Plains and helping to consolidate/strengthen a surface
frontal system. This will lead to enhanced lift over the Northern Plains
and a quick developing and potentially intense band of snowfall by
Wednesday evening. Snow totals of 2-4″ can be expected with locally
heavier amounts possible through Thursday morning. Some mixed
precipitation with light ice accumulations will be possible as well.

Elsewhere, persistent shower and thunderstorm chances will continue for
Florida, particularly along the Atlantic Coast. Some intense downpours
will be possible Tuesday with an isolated threat of some flooding in the
urban areas of South Florida. Most of the country will continue to see
well above average temperatures through at least mid-week. Forecast highs
Tuesday range from the 40s and 50s in the interior West and New England;
the 50s and 60s for the West Coast, central Plains, Ohio Valley, and
Mid-Atlantic; and 60s and 70s for the Southwest, southern Plains, and
Southeast. A cold front will bring some cooler, more seasonable
temperatures to the Plains Wednesday as highs fall into the 40s and 50s.
One region that will remain much colder will be the Northern Plains/Upper
Midwest, with most highs only into the teens and 20s.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Dec 16 2024
Valid 12Z Mon Dec 16 2024 – 12Z Wed Dec 18 2024

…Modest atmospheric river activity to bring unsettled weather to the
Northwest, including heavy rains for the coastal ranges and accumulating
snow for the higher elevations…

…Wet conditions expected for much of the eastern half of the country the
next couple of days…

…Above average temperatures, mild conditions expected for much of the
country to start the week…

A pair of Pacific systems will help to focus a flow of moisture over the
Northwest in an active Atmospheric River pattern the next couple of days.
Precipitation continues this morning as moisture flows inland from the
first system bringing moderate to heavy coastal rain, an inland wintry
mix, and heavy higher elevation mountain snow across the Pacific
Northwest, northern California, and the northern Great Basin/Rockies. The
heaviest precipitation will be focused southward today across
Oregon/northern California and inland through central Idaho into northwest
Wyoming. The focus will shift northward on Tuesday bringing heavier rain
to coastal Washington state as well as heavy snow to the northern
Cascades. Snow totals of 4-8″ will be common with locally higher totals
over a foot for the highest peaks expected, particularly for the southern
Cascades in Oregon Monday.

To the east, light to moderate rainfall continues this morning over the
Mid-Atlantic with some wintry precipitation over the Interior Northeast,
which should taper off through early afternoon. A more focused corridor of
showers and thunderstorms will redevelop through the day ahead of a cold
front over the Ohio Valley southwestward through the Lower Mississippi
Valley/Southern Plains. Some moderate to locally heavy rainfall will be
possible, particularly for the Ohio Valley. This system will bring another
wave of rain through the Mid-Atlantic Monday evening and New England
Tuesday morning, with a wintry mix possible for interior locations. An
approaching upper-level wave will help to kick off another round of
showers and storms along the frontal boundary from the Ohio Valley
southwest through the Southern Plains Tuesday.

Elsewhere, an upper-level wave passing over the Northern Plains/Upper
Midwest will bring some snow showers on Tuesday with some light
accumulations possible. Some lake effect snow showers are also expected to
continue downwind of the Great Lakes, particularly Lakes Erie and Ontario.
Daily shower and thunderstorm chances are forecast for the Florida
Peninsula with coverage and intensity increasing on Tuesday along the
Atlantic Coast. Much of the country will see high temperatures above
average with generally mild conditions. Some of the greatest anomalies
will be over the Midwest Monday as highs climb into the 50s, and over the
Northeast Tuesday with highs into the 50s and 60s. Frontal passages will
lead to more temperature fluctuation along the northern tier of the
country while the southern tier will remain more stable, with daily highs
generally in the 60s and 70s.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Sun Dec 15 2024
Valid 12Z Sun Dec 15 2024 – 12Z Tue Dec 17 2024

…Wintry mix expected for the Appalachians Sunday with the potential for
significant icing in the central Appalachians…

…Showers and storms with locally heavy rainfall possible across the
Lower Ohio Valley through Monday…

…Pacific system to bring a renewed round of lower elevation/coastal rain
and heavy mountain snow to the Northwest late Sunday into Monday…

An upper-level wave has helped trigger a broad area of wintry
precipitation this morning which will pass through the interior
Northeast/Appalachians through the day Sunday. Some light snow
accumulations will be possible for the central/northern Appalachians with
some ice accretions expected for the southern/central Appalachians. More
significant ice accretions of 0.1-0.3″ are forecast for a smaller region
of eastern West Virginia north through western Maryland and into southwest
Pennsylvania which could cause tree and power line damage. Some lighter
rain showers will be possible along the Eastern Seaboard. The wintry
precipitation will lift northward into New England bringing some lighter
accumulations into the day Monday.

Further West, another upper-level wave/accompanying surface frontal system
will better organize along the High Plains and push eastward into the
Plains Sunday. Some light snow/ice accumulations will be possible
northwest of the system over portions of the northern Plains through
Sunday evening before shifting into the Upper Midwest Monday. To the
south, moist return flow form the Gulf reaching the eastward moving
frontal system will lead to increasing coverage of showers and
thunderstorms across the Lower Ohio Valley southwest into the Southern
Plains by late Sunday. Coverage and intensity should increase through the
day Monday as the front pushes southeastward into the Tennessee Valley and
Lower Mississippi Valley through Monday evening. Some locally heavy
rainfall will be possible, particularly across the Lower Ohio Valley
Monday. Showers are also expected to spread eastward into the Northeast
Monday.

Some moderate to locally heavy snow will continue through Sunday morning
for higher mountain elevations of the northern Rockies/Great Basin as well
as for the Cascades as an upper-level trough departs the region.
Precipitation should generally tend to taper off through the afternoon.
However, another Pacific system approaching the Pacific Northwest/northern
California will bring a renewed round of precipitation spreading inland
through the Northwest by Sunday night. Moderate to heavy lower
elevation/coastal rain, a wintry mix for inland valleys, and moderate to
heavy mountain snow can all be expected through Monday. The heaviest snow
totals of 8-12″, locally higher, are most likely from the southern
Cascades/northern California east through Oregon into central Idaho and
northwest Wyoming. Some gusty winds can also be expected along the Pacific
Coast.

Elsewhere, some showers and thunderstorms will be possible along the east
coast of Florida north through the Carolinas the next couple of days.
Temperature-wise, conditions will generally be at or above average for
most of the country. Some of the most anomalous temperatures will be over
central portions of the country, with highs in the 60s and 70s for the
Southern Plains Sunday and highs into the 50s for many in the Midwest on
Monday. One of the cooler spots will be along the East Coast as cold air
remains in place along the Appalachians Sunday, with highs in the 30s and
40s as far south as the western Carolinas and northern Georgia.
Temperatures will warm above average here as well on Monday with highs
reaching into the 40s and 50s.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Sat Dec 14 2024
Valid 12Z Sat Dec 14 2024 – 12Z Mon Dec 16 2024

…Atmospheric River continues to bring very heavy rain with the potential
for flooding, heavy mountain snow, and gusty winds to central/northern
California Saturday…

…Heavy mountain snow forecast for portions of the Great Basin and
northern Rockies Saturday…

…Wintry mix including accumulating freezing rain continues for portions
of the Upper Midwest Saturday, spreading into the central Appalachians
Sunday…

A Pacific storm system and accompanying strong flow of
moisture/Atmospheric River continues inland over the West this morning
(Saturday) bringing heavy rainfall, mountain snow, and gusty winds to
central/northern California and the Pacific Northwest. The heaviest
rainfall will continue to focus on portions of central/northern California
through Saturday morning where rainfall rates of 0.5″ to 1″ per hour will
lead to an additional few inches of rainfall over already saturated
ground. The greatest potential for flooding will be around the greater Bay
Area where a Slight Risk of Excessive Rainfall (level 2/4) is in effect.
Heavy snowfall will also continue for higher mountain elevations of the
Coastal Ranges and Sierra Nevada, generally over 5000 feet, where Winter
Storm Warnings have been issued for storm total snowfall of 1-3 feet.
Winter Weather Advisories are also in effect further north into the
Cascades where storm total snowfall of 8-12″, locally 18″, can be
expected. Gusty winds also continue this morning, particularly along the
coast, but all hazardous impacts from the system should begin to taper off
through Saturday afternoon.

The system will push further inland through the day Saturday, spreading
moisture and precipitation chances across the Great Basin and Northern
Rockies. A mix of rain and snow can be expected at lower elevations,
though any snow accumulations should remain limited. Heavier snow is
forecast in the mountains, particularly from central Idaho into western
Wyoming, where Winter Storm Warnings are in effect for snowfall of 5-10″,
locally 12″+. Precipitation chances will spread eastward into the northern
High Plains by Saturday night with a wintry mix expected. Some light ice
accretions will be possible through the day Sunday. Some gusty winds are
also likely along the Front Range of the Rockies as the system pushes out
onto the Plains.

Further east, an upper-level shortwave/accompanying surface frontal system
will help to trigger showers and thunderstorms across the Ohio, Middle
Missouri, and Lower Mississippi Valleys Saturday, with some moderate to
locally heavy rainfall possible. Storms will likely linger into Sunday
along a trailing frontal boundary, though with lighter amounts expected.
More impactful weather will continue further north as warmer, moist air
overrides colder air at the surface leading to a wintry mix across the
Upper Midwest and Great Lakes. Snow/sleet accumulations should remain
light, but freezing rain is also expected, particularly over eastern Iowa.
An Ice Storm Warning remains in effect through Saturday afternoon for
totals potentially exceeding 0.25″ and leading to tree and power line
damage. The system will continue east on Sunday bringing a wintry mix into
the Southern Appalachians. Similar to Saturday, snow/sleet accumulations
should generally remain light, but some ice accretions over 0.1″ will be
possible.

Elsewhere, some showers and thunderstorms can be expected this weekend
along the Atlantic Coast of the Southeast and Florida with a
quasi-stationary frontal boundary in place. Additionally, after a brief
break late Saturday/early Sunday, another system over the Pacific will
bring increasing precipitation chances back to the Pacific Northwest by
Sunday evening. Most of the country will see high temperatures at or above
average this weekend as conditions moderate following a cold frontal
passage across the South and with an upper-level ridge passing over the
central/western U.S. ahead of the next Pacific system. Some of the warmest
temperatures will be in the Southern Plains/Texas with highs in the 60s,
70s, and even some low 80s. Otherwise, temperatures generally range from
the 30s and 40s from the Pacific Northwest and Great Basin east through
the northern Plains, Great Lakes, and Northeast; the 50s and 60s for
California, the central Plains, Ohio Valley, and the South; and 70s for
the Desert Southwest and Florida.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Fri Dec 13 2024
Valid 12Z Fri Dec 13 2024 – 12Z Sun Dec 15 2024

…Atmospheric River to bring very heavy rainfall and possible flooding as
well as high elevation mountain snow to the West Coast…

…Heavy mountain snow forecast for portions of the Great Basin and
northern Rockies Saturday…

…Potentially impactful wintry mix with freezing rain expected across the
Middle Missouri Valley and Upper Midwest Saturday…

An Atmospheric River event will bring very heavy rain, mountain snow, and
gusty winds to portions of southern Oregon and northern/central California
Friday into Saturday. A Slight Risk of Excessive Rainfall (level 2/4) has
been issued along portions of the Coastal Ranges of northern California
where locally heavy rainfall rates of 0.5″ per hour and rainfall totals of
3-5″, with isolated higher amounts upwards of 7″, may lead to some
instances of flooding during the height of the event Friday
evening/overnight into Saturday morning. Very heavy mountain snow is
expected at higher elevations (generally over 5000-6000 feet) of the
Coastal Ranges and for the Sierra Nevada. Winter Storm Warnings have been
issued for forecast snowfall totals of 1-2 feet, locally higher. In
addition to the heavy precipitation, strong, gusty winds are also
expected, particularly for coastal locations. A broader area of more
moderate rainfall stretches across the Pacific Northwest and south along
coastal California. Some Moderate to heavy snow is also forecast further
north through the Cascades where 4-8″, locally higher, can be expected.
The system will continue eastward late Friday and into the day Saturday,
spreading moisture and precipitation chances further inland over the Great
Basin and northern Rockies. A mix of rain and snow can be expected at
lower elevations with snow, heavy at times, for higher mountain
elevations. Winter storm Watches have been issued for the mountains of
central Idaho where the heaviest snow is expected with forecast totals of
6-12″.

To the east, an upper-level wave passing from the Rockies and over the
Plains will help to organize a surface frontal system and encourage moist,
southerly return flow from the Gulf of Mexico. Showers and thunderstorms
are forecast ahead of an eastward moving cold front across eastern
portions of the central/southern Plains on Friday. More widespread storms
with moderate to locally heavy rainfall are expected on Saturday as the
system continues into the Middle Mississippi/Lower Ohio Valley. Some
potentially impactful winter weather is forecast further north across the
Middle Missouri Valley and into portions of the Upper Midwest where warm,
moist air overriding colder temperatures will lead to a wintry mix Friday
afternoon through Saturday. Snow/sleet accumulations should remain light,
but some freezing rain accretions are also expected. These accretions may
be greater than 0.1″ over eastern Iowa which could lead to some tree
damage and power outages. Regardless, the wintry mix will at least likely
lead to some travel troubles across the region.

Elsewhere, most lake effect snow will be tapering off Friday morning for
the Great Lakes except downwind of Lake Ontario where an additional 6-12″
can be expected through the day Friday. Some light to moderate snow
showers will also continue through the day Friday for the central Rockies
as a cold front moves through the region. High temperatures will remain
cold and below average for much of the north-central and eastern U.S.
following a frontal passage. Forecast highs range from the teens and 20s
for the northern Plains, Great Lakes, and interior Northeast; the 30s and
40s for the Ohio Valley and Mid-Atlantic/coastal Northeast; and the 50s
across the Southeast. Conditions will moderate closer to average Saturday
with highs generally running 5-15 degrees warmer. Forecast highs are
generally at or above average across the West, with 40s and 50s in the
Pacific Northwest, Great Basin, and Rockies; the 50s and 60s in
California; and the 70s in the Desert Southwest. Conditions in the
Southern Plains/Texas will be some of the warmest and most above average
compared to the rest of the country with highs into the 60s and 70s.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Thu Dec 12 2024
Valid 12Z Thu Dec 12 2024 – 12Z Sat Dec 14 2024

…Great Lakes heavy lake-effect snow expected to continue into Friday
especially along the Snow Belt of the lower Great Lakes…

…A couple rounds of heavy coastal rain and heavy mountain snow expected
to impact northern California into Sierra Nevada heading into the
weekend…

…Sub-zero temperatures expected over parts of the northern Plains and
upper Mississippi Valley for the next couple of mornings…

As a deep low pressure system races further northward into eastern Canada
and a potent cold front exits New England this morning, an arctic high
pressure system will take over the northern Plains and expand across the
entire eastern U.S. through the next couple of days. Maine will be the
last to clear out from the heavy rain early this morning followed by much
colder temperatures under blustery westerly winds. The resurgence of
arctic air is triggering a new round of heavy lake-effect snow across the
Great Lakes through today and tonight before gradually tapering off on
Friday. The Snow Belt of the lower Great Lakes can expect a foot or more
of new snow, with locations downwind from Lake Ontario possibly getting
more than 2 feet since these locations will be the last to clear out from
the snow late on Friday.

Along the West Coast, moisture ahead of the next Pacific cyclone is poised
to overspread much of the Pacific Northwest and a good portion of
California today. The heaviest precipitation is expected to reach
northern California in form of rain near the coast and lower elevations.
A quick round of moderate to heavy snow will then reach the high
elevations farther inland and then along the Sierra Nevada for much of
today. It appears that this latest around of precipitation will taper off
temporarily tonight before the next round of precipitation associated with
the next Pacific cyclone arrives on Friday. Northern California into
southwestern Oregon can expect heavy precipitation Friday night with a
marginal risk of excessive rainfall continuing into Saturday morning by
the end of the short-range forecast period. Lesser amounts of
precipitation are expected for the Pacific Northwest.

The arctic high pressure system that is forecast to bring sub-zero
temperatures for the next couple of mornings is forecast to strengthen and
slide east into New England by Saturday morning. This will allow
southerly flow to increase across the southern Plains along with moisture
returning from the Gulf of Mexico by Friday night. Meanwhile, residual
energy associated with the first Pacific system is forecast to exit the
southern Rockies and induce the formation of a low pressure system over
the central Plains by Friday night. Some thunderstorms along with heavy
rain could quickly develop and move across the central Plains early on
Saturday ahead of the new low pressure system. Colder air could support
areas of mixed rain and snow farther north across the north-central Plains
into the upper Midwest in advance of the low pressure center. In the
short-term though, dry, breezy and relatively mild conditions will support
elevated fire danger across the southern High Plains for today.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Wed Dec 11 2024
Valid 12Z Wed Dec 11 2024 – 12Z Fri Dec 13 2024

…Widespread heavy rain and severe thunderstorm treats spreading up the
East Coast today and through New England into tonight…

…A surge of cold air into the eastern U.S. today will be followed by a
reinforcing surge of arctic air into the northern U.S. through the next
couple of days…

…Another round of significant lake effect snow expected through the next
couple of days downwind of the Lakes...

The stage is set for a rapidly intensifying low pressure system to track
up the East Coast today. A potent cold front trailing southwest from the
center of this elongated low pressure system will be the focus for heavy
rain, blustery winds, and strong to severe thunderstorms. Ahead of the
front, warm and moist air streaming in from the nearby Atlantic and Gulf
of Mexico will interact more vigorously with a jet stream aloft to develop
and expand the coverage of showers and thunderstorms, first across the
Southeast and the Carolinas this morning, followed by the Mid-Atlantic
states during the day, and into New England this evening. The highly
dynamic nature of this front will likely trigger formation of strong to
severe thunderstorms. This is especially the case across eastern North
Carolina this afternoon, and into southern New England this evening, where
the Storm Prediction Center has issued a Slight Risk (level 2 of 5) for
severe thunderstorms capable of producing damaging wind gusts. Elsewhere
along the Eastern Seaboard, the main concern will be a period of heavy
rain with embedded strong thunderstorms and intense downpours. Despite
much of the region currently experiencing moderate to extreme drought
conditions, the rain, while mostly beneficial, could lead to some
localized instances of flash flooding. The more urbanized locations and
poor drainage areas would have the greater risk of flooding issues.

Behind the potent cold front sharply colder air will surge into the East
Coast from the north and northwest. A period of accumulating wet snow can
be expected to spread up the western slope of the entire spine of the
Appalachians from south to north today through tonight. Meanwhile, a
reinforcing shot of arctic air is plunging into the northern Plains and
will overspread much of the northern tier states through the next couple
of days. High temperatures the next couple of days will be roughly 10 to
as much as 30 degrees below normal.

Attention then turns to yet another round of significant lake effect snow
downwind of the Great Lakes through the next couple of days. The
aforementioned surge of arctic air will stream across the still relatively
warm Great Lakes and ignite intense bands of lake effect snow, initially
downwind of Lakes Superior and Michigan on today and then downwind of
Lakes Erie and Ontario tonight into early Thursday. By the time the snow
starts to taper off on Friday, snowfall totals of 1 to 2 feet are likely
in the favored Snow Belt across portions of northwest and western New York
State, far northwest Pennsylvania, far northeastern Ohio, the Upper
Peninsula of Michigan and the western portions of the Lower Peninsula of
Michigan.

Along the West Coast, moisture ahead of the next cyclone from the Pacific
is poised to overspread much of the region through the next couple of
days. Northern California will see heavy coastal rain by this evening,
followed by heavy mountain snow farther inland and down the Sierra Nevada
where a foot or more of new snow is forecast through Thursday. It appears
that this round of precipitation will mostly taper off Thursday night
prior to the arrival of the next Pacific system.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Tue Dec 10 2024
Valid 12Z Tue Dec 10 2024 – 12Z Thu Dec 12 2024

…Widespread heavy rain threat emerging across the central to eastern
Gulf Coast region today will spread rapidly up the entire East Coast on
Wednesday…

…Active Lake effect snows to begin Wednesday and continue through
Thursday downwind of the Lakes…

…Record warm morning lows likely along the east coast Wednesday
morning…

…Arctic air to surge south into the Northern Plains/Upper Mississippi
Valley region late Tuesday into Wednesday…

…Santa Ana winds along with critical to extreme fire weather danger
across portions of southern California…

The upper-level flow pattern across much of North America will undergo
significant amplification over the next few days, producing various types
of impactful weather across mainland U.S. The most active weather in
terms of precipitation and winds will be the primary focus along the East
Coast through the next couple of days. Precipitation currently falling
across portions of the Southeast is in its organizing stage ahead of a
developing low pressure wave over the Mid-South along a cold front. As
the cold air behind the front interacts with a rapidly amplifying upper
trough, rain and embedded thunderstorms will rapidly expand northeastward
during the day Wednesday and up the entire East Coast, producing a period
of widespread heavy rainfall from the central to eastern Gulf coast,
across the Southeast, Mid-Atlantic, Northeast and New England. With much
of these areas currently in moderate to extreme drought conditions, this
rainfall will be beneficial. Still, given the potential for periods of
heavy rains over a short period, there will be a threat of localized flash
flooding, especially in more urbanized regions.

The cold front associated with this rapidly intensifying system will
become rather potent as it sweeps across the East Coast during the day on
Wednesday. There is potential for some very strong thunderstorms to form
ahead of the front together with heavy downpours. Meanwhile, drastically
colder air behind the front is forecast to produce accumulating snowfall
up the western slopes of the Appalachians on Wednesday together with
blustery northwesterly winds. The snow will then sweep across interior
New England through Wednesday night into Thursday morning as a potent
elongated low pressure system races northward into southeastern Canada.

With a warm southerly flow strengthening ahead of this potent front, there
is the potential for widespread record high morning low temperatures on
Wednesday across the southern Mid-Atlantic, Mid-Atlantic and portions of
the Northeast. In the wake of this front, much colder air will stream
across the Great Lakes from west to east beginning on Wednesday. This will
ignite active lake-effect snows, initially downwind of Lakes Superior and
Michigan on Wednesday and then downwind of Lakes Erie and Ontario
Wednesday night into early Thursday. Before these lake-effect snows
diminish by early Friday, snowfall totals of 1 to 2 feet are possible in
the favored Snow Belt across portions of northwest and western New York
State, far northwest Pennsylvania, far northeastern Ohio, the Upper
Peninsula of Michigan and the western portions of the Lower Peninsula of
Michigan.

The above-mentioned lake-effect snows will be driven by arctic air that
will be first surging east southeastward late Tuesday into early Wednesday
across the Northern Plains into the Upper Mississippi Valley and then
eastward trough the Great Lakes into the Ohio Valley on Wednesday. While
there are not expected to be any records with this arctic outbreak,
temperatures will be much below average on Wednesday across the Northern
Plains into the Upper Mississippi Valley. These much below average
temperatures will then push farther southeast into the Great Lakes and
Ohio Valley region on Thursday. Across these regions, high temperatures
will be 10 to 25 degrees below average during the height of the cold
temperatures during Wednesday and Thursday.

In contrast to the wet and cold conditions across portions of the
north-central to eastern U.S., dry condition and milder temperatures are
in store across the West coast, Great Basin and Rockies region. The dry
air, low relative humidities together with the latest episode of Santa Ana
winds across southern California will produce critical to locally extreme
fire weather danger. These fire weather conditions will be most prominent
in the higher terrain areas to the north and east of the Los Angeles to
San Diego region. Winds of 35 to 45 mph in the valleys and gusts of 50 to
65 mph in the mountains will help fan any fires that do develop quickly
and may reduce visibility with blowing smoke and dust adding to travel
concerns in the region. Across these areas, red flag warnings are
currently in effect, affecting nearly 13 million people.

By early on Thursday, the next round of coastal rain and mountain snow is
forecast to reach northern California as the next Pacific cyclone arrives.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Dec 09 2024
Valid 12Z Mon Dec 09 2024 – 12Z Wed Dec 11 2024

…Heavy rain threat across the central to eastern Gulf Coast region today
will expand and move up the East Coast late Tuesday into Wednesday
morning…

…Periods of mixed rain and snow linger across interior New England
through tonight…

…Snow/blizzard conditions across the northern High Plains will gradually
taper off later today…

…Strong Santa Ana winds prompting critical fire danger across Southern
California…

…Well above average temperatures will overspread the central and eastern
U.S. as cold air surges into the western and then central U.S….

Increasingly active weather will progress toward the eastern U.S. through
the next couple of days as a weather pattern reversal continues to unfold
across the mainland U.S. One of the ingredients of this pattern change is
manifested by an expanding area of moderate to heavy rain moving through
the Ohio and Tennessee Valleys this morning with embedded thunderstorms
across the Deep South. The associated jet stream aloft will send the rain
rapidly northeastward across the Mid-Atlantic states today, reaching into
southern New England tonight. Temperatures will be cold enough to support
snow across northern New England Monday night into Tuesday morning before
tapering off for the time-being Tuesday afternoon. Meanwhile, an
extensive surge of cold air into the mid-section of the country will
reinvigorate the jet stream across the Deep South on Tuesday, leading to
an expanding area of moderate to locally heavy rain from the Gulf Coast
into the Deep South and interior Southeast. Tuesday night into Wednesday
morning will likely see the rain quickly expanding up the Appalachians and
into the interior section of the Mid-Atlantic, and then up into New
England with some ice possible at the onset. Meanwhile, organized lines
of thunderstorms could form ahead of a potent cold front across the
interior Southeast early on Wednesday along with sharply colder
temperatures and blustery northwesterly winds behind the front.

Across the northern High Plains, colder air and gale force winds behind a
low pressure system have prompted winter weather advisories/warnings,
Blizzard Warnings, as well as wind advisories/high wind warnings this
morning. 4-7″ of snow is expected across the northern High Plains.
Meanwhile, strong onshore flow off Lake Superior will further enhance
local snow totals across the Arrowhead of MN range where 9-12″+ totals are
expected.

On Tuesday, a more intense surge of cold air will be funneled southward
from Alaska and western Canada into the Plains associated with an
intensifying arctic high pressure system. A ‘Blue Norther’ cold front
will be driving well through the Southern Plains into northern Mexico by
Tuesday night, dropping temperatures into the 30s into southern Texas by
Wednesday morning. Meanwhile, a reinforcing cold front will drop
temperatures below zero degrees over the northern Plains by then. High
temperatures will be about 5-10 degrees below normal across much of the
Rockies, Southwest and eventually into the Plains.

Across the western U.S., a cold surge directed through the Great Basin
into the lower Colorado River Valley today will bring very strong Santa
Ana winds into southern California by later today. Given dry/low humidity
conditions already in place, Red Flag Warnings have been issued for the
eastern Transverse and all of the Peninsular Ranges; as well as a Critical
Fire (level 2 of 3) from the Storm Prediction Center. Winds of 35 to 45
mph in the valleys and gusts of 50 to 65 mph in the mountains will help
fan any fires that do develop quickly and may reduce visibility with
blowing smoke and dust adding to travel concerns in the region.