FOUS11 KWBC 100955
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
454 AM EST Wed Jan 10 2024

Valid 12Z Wed Jan 10 2024 - 12Z Sat Jan 13 2024

...Great Lakes and Northeast...
Days 1-2...

Strong surface low will be positioned near eastern lower Michigan
to start the period, but will translate rapidly northeast with
time through D1. This storm is quite wrapped up owing to an
anomalous closed mid-level low directly overhead, and a strong
secondary vorticity maxima rotating northeast into New England
producing a strongly negative tilt. The vertical stack of the
primary low will allow a secondary low to develop along the
occlusion to the east, driving the most intense moisture advection
into New England and then Canada by the end of D1. This moisture
transport will remain exceptional, with IVT anomalies from NAEFS
reaching +6 sigma over ME early on D1 before pivoting off into
Canada the latter half of the day. This suggests the heaviest
precipitation will be in northern New England, primarily in the
higher terrain of ME, as strong accompanying WAA warms snow levels
above 4000 ft, but WPC probabilities for additional snowfall
exceeding 4 inches are only 20-30%, and only around Mt. Katahdin
and Mt. Washington.

As the low pulls away to the northeast, impressive CAA will
develop on increasing N/NW winds which will support increasing
coverage of lake effect snow (LES) downstream of the Great Lakes.
Overall, LES appears modest in most areas as shortwave ridging
returns quickly into D2. However, the most impressive LES is
likely downstream of Lake Ontario into the Tug Hill Plateau where,
despite this secondary shortwave approaching to locally back the
mid-level flow to more W/SW, this will still support cool air
moving across the long fetch of Lake Ontario to support heavy LES.
WPC probabilities D1 and D2 exceed 80% for 4 inches both days.

...Central Plains to the interior Northeast...
Days 2-3...

A shortwave diving into the Pacific Northwest Thursday will race
southeast across the Great Basin to reach the Southern Plains on
Friday. This will drive a deepening longwave trough across the
Intermountain West, with this trough pivoting eastward and
elongating with time. As the primary vorticity maxima associated
with the potent shortwave rounds the base of this trough and tilts
negatively before closing off later Friday, the central part of
the country will become entrenched within a potent and persistent
trough to support yet another winter storm arcing from the Plains
into the Northeast beginning Thursday night.

The surface low is likely to develop Thursday evening in the lee
of the Southern Rockies in response to PVA/height falls downstream
of the potent shortwave, and within an area of increasing upper
diffluence as a jet streak intensifies downstream of the longwave
trough axis. Moisture will begin to return out of the Gulf on
moistening 290-295K isentropic upglide, which will combine with SE
700-500mb flow around the trough to surge PWs to +1 to +2 sigma
according to NAEFS, highest across the lower MS VLY D2 and into
the western OH VLY D3. This moisture will be acted upon by
strengthening synoptic deep layer lift as the upper trough tilts
negatively, and a coupled jet structure develops overhead and
efficiently overlaps the greatest height falls. This suggests that
the surface low will strengthen rapidly as it shifts northeast
towards the Great Lakes by D3, with a large shield of
precipitation expanding along its track.

There remains considerable uncertainty into the exact track of
this storm both in the deterministic models and the ensemble
clusters, some of which is likely due to the impacts of the
preceding storm and where it lays its residual baroclinic
gradient. However, regardless of the exact track of this system,
it is likely that along and north of the track, especially beneath
what should become an intense TROWAL, heavy snowfall will occur.
The synoptic evolution should support heavy snow bands both within
the leading WAA, and again within any deformation axis that could
develop on the NW side of the mature cyclone, especially by D3. It
is too early to determine exactly where those will setup, but this
is likely to be a strong and large-scale system with heavy snow
spreading from portions of the Central Plains through the Great
Lakes. WPC probabilities D2 for more than 4 inches of snow are
40-70% in a narrow corridor focused around southeast Nebraska,
before expanding considerably into D3 reaching above 50% from
central Missouri through much of the Great Lakes region. Locally
much higher totals are likely, reflected by WPC probabilities for
more than 12 inches on D3 exceeding 40% from near Chicago and
Milwaukee through much of the L.P. of MI.

Additionally, later on D3, as the primary low occludes to a
secondary triple point to its east, the best moisture flux should
shift into New England where once again robust WAA should result
in heavy snowfall in the higher elevations of Northern New
England. WPC probabilities for more than 4 inches of snow are
50-70% in the higher terrain of the Adirondacks, Greens, and
Whites.

Regardless of exactly where this system tracks, impacts are likely
to be substantial as reflected by the WSSI-P indicating already a
large area of 30-50% probabilities for moderate impacts due to
snow rate, snow amount, and blowing snow.

...The West...
Days 1-3...

An extremely active pattern continues across the Pacific Northwest
and into the Northern Rockies/Great Basin through late week as a
series of shortwaves drop onshore from the Pacific.

The first of these systems is moving onshore this morning and will
drive a surface low/associated cold front through the Pacific
Northwest and as far southeast as the Central Rockies by
tonight.This is a potent shortwave but gets sheared out into
significantly confluent mid-level flow as the longwave trough
amplifies. This shortwave will dive all the way into the southern
Great Basin by D2, and while it will weaken within the positively
tilted trough, and encounter only modest available moisture, heavy precipitation is likely to extend as far southeast as the CO
Rockies, with snow generally occurring above 1500 ft. WPC
probabilities for snow exceeding 6 inches eclipse 80% along the
Cascades and down into the Sierra, as well as into the Blue
Mountains, higher terrain of the Great Basin, and into the
Wasatch. Locally, more than 2 feet of snow is possible in the
highest terrain of the Cascades and Sierra, and with snow levels
crashing late D1, light snow accumulations are possible across
many of the lower valleys as well.

As that first trough digs across the Four Corners and intensifies
into the next central U.S. low, the pattern begins to shift as the
primary trough amplifies over Alberta and then digs southward,
driving a surface cold front into a more NW to SE orientation as
it drops into WA/ID/MT on Thursday. South of this trough,
mid-level flow becomes increasingly pinched with W/NW flow
impinging again into the Cascades and then spilling southeast
across much of the West as the front sags southward. Although IVT
will remain modest at less than 250 kg/ms according to NAEFS,this
increasing moisture being acted upon by intensifying fgen along
the cold front and amplifying upper diffluence ahead of an
approaching jet streak should result in widespread snowfall once
again spreading across the Northwest. As the pattern continues to
evolve into D3, another shortwave approaching the Pacific
Northwest coast will drive more impressive mid-level confluence,
and the overlap of this pinched flow with the eastward translation
of the upper jet will drive IVT to above 500 kg/ms, resulting in
much more significant available moisture for precipitation. At the
same time the cold front will be sharpening and dropping farther
south, driving better ascent and lowering snow levels to the
surface as far south as a roughly Portland, OR to Cheyenne, WY
line. This strong ascent, steep lapse rates beneath the cold pool,
lowering snow levels, and ample moisture, will produce heavy snow accumulations, spreading southeast with time. On D2 WPC
probabilities for more than 6 inches exceed 80% in the Cascades,
Blue Mountains, Salmon River/Sawtooth region, and the Northern
Rockies, with 2+ feet probable in the higher terrain. During D3
the greatest WPC probabilities shift south slightly, focusing in
the OR Cascades and east across the northern Great Basin into the
Tetons and Wasatch. Again on D3, local totals exceeding 2 feet are
likely. Additionally, especially by D3, with snow levels
collapsing towards the surface, moderate accumulations are
becoming more likely in the valleys and lowlands, with Seattle, WA
and Portland, OR both featuring 30-40% probabilities for at least
2 inches of snowfall.

Finally, the strong cold front moving across Oregon this morning
will continue to shift rapidly southeast across the Great Basin
and into the Central Rockies by Thursday morning. This could
spread convective snow showers and snow squalls across the area,
with the CIPS snow squall parameter showing values above +1
spreading as far south as the Four Corners states. Evaluation of
the fields which drive the snow squall parameter indicate the
threat has increased this morning as the coverage of overlapping
sufficient 0-2km RH/925mb fgen/SBCAPE>100 J/kg to support intense
squalls is more widespread, especially along and immediately
behind the front. Snow squalls should still generally be
scattered, but more numerous convective snow showers are also
likely which could cause brief but significant travel disruptions
due to gusty winds and heavy snow rates.

Weiss

***Key Messages for Jan. 8-13 Major Winter Storm***
--Continuing Blizzard Impacts in the Northwest
Periods of heavy snow will continue through this afternoon in the
Northwest. An additional 6-12 inches of snow will bring storm
total accumulations to several feet in the higher elevations of
the Cascades and Olympics. Gusts to at least 60 MPH will create
blizzard conditions, continuing considerable travel impacts for
many mountain passes.

--Heavy Snow in the Sierra
Heavy snow rates of 1-2"/hr will cause significant snowfall
accumulations likely (70-90%) exceeding 12 inches in the Sierra
today. Strong winds of 40-50 MPH during the heaviest snow will
produce difficult travel.

--Snow squalls across the Great Basin and Four Corners
Snow squalls are likely behind a cold front through tonight. These
intense bursts of snow pose a significant danger to motorists as
rates of 1-2"/hr combine with strong wind gusts to produce rapid
changes in visibility, occasional whiteouts, and possible flash
freezes on roadways.

--Significant Central U.S. winter storm begins Thursday night
Confidence has increased that this system will emerge into the
Plains Thursday and strengthen into a potent winter storm by
Friday. Uncertainty continues in the track and intensity of this
system, but a swath of heavy snow is likely from the Central
Plains through the Great Lakes where the probability of exceeding
4 inches is above 70% from eastern Nebraska through lower
Michigan. Considerable blowing and drifting of this snow in strong
winds also possible.
$$
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FOUS11 KWBC 110857
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Thu Jan 11 2024

Valid 12Z Thu Jan 11 2024 - 12Z Sun Jan 14 2024

...Great Lakes and Northeast...
Day 1...

Well-defined shortwave trough over southern WI will quickly shift
east across MI and the Northeast today given the strengthening jet
to its south while another impulse over northeast ND will drift
east across northern MN today. Both will produce Great Lake
enhanced snow today with 40-60% Day 1 snow probs for >6" over the
North Shore of MN and 40-60% probs for >4" east of Lakes Erie and
Ontario for westerly flow lake enhanced snow this
afternoon/evening in NY.

...Central Plains, Great Lakes and interior Northeast...
Days 1-3...

A digging trough crossing AZ today will take on a negative tilt
after crossing the southern Rockies this evening as a
double-barreled jet becomes more buckled and S-shaped across the
Great Lakes into Friday. This will drive strong upper level
divergence and rapid surface cyclogenesis with a deepening area of
low pressure lifting Friday from the Ozarks through the Midwest
and over the L.P. of MI Friday night. This is a strikingly similar
track to the exiting system though it forms farther east over the
Plains). Snow will rapidly increase in coverage and intensity
north of the low this evening over the central Plains and then IA
through MI late tonight through Friday evening. As the low tracks
away on Saturday, intense lake-effect snow develops, covering all
five Great Lakes by Saturday night.

Initial WAA over colder sfc air tonight will likely support a
wintry mix in the rain to snow transition zone from northeast KS
into northern IL. North in the snow zone, significant snowfall is
expected on the northwest side of the low as a deformation band
forms and slowly pivots across the area, coincident with an
intense TROWAL as the WCB wraps into the low. High-end potential
is >18" per PWPF from peak development and lake enhancement in
southeast WI and northeast portions of the L.P., driven by strong
UVV into a sufficiently deep DGZ. Day 1.5 snow probs for >8" are
20-50% from eastern Neb through central IA, increasing on the Day
2 to 40-90% from the WI/IL border across the L.P. The powerful
cyclone reaches peak intensity over the L.P. Friday night with
MSLP in the low 970s making for very strong winds and a blizzard
threat north and west of the low through this time.

Strong northwest to west flow on the back side of the low
envelopes the Great Lakes in the wake with LES beginning off Lake
Superior Saturday and the rest of the Great Lakes by late Saturday
night and continuing in earnest through at least Sunday night. Day
3 snow probs for >6" are 40-80% for typical NW and W snow belts.

On the eastern side, cold air mass in place will slowly be eroded
as broad southerly flow once again erodes sub-freezing
temperatures. The uneven erosion in the column will likely lead to
a period of snow to freezing rain to rain in most areas outside
northern Maine as a triple point low moves across the area. Before
the changeover, several inches of snow will likely accumulate over
terrain in interior portions of the Northeast with Day 2.5 WPC
snow probabilities for >6" are 40-80% over the Adirondacks and
White Mtns.

...The West...
Days 1-3...
Active winter pattern continues over The West through this weekend.

A positively-tilted trough digging down the Sierra Nevada early
this morning crosses Arizona today and the southern Rockies this
evening. Snow levels around 4000ft along the Mogollon Rim and
north-central NM ranges along with decent Pacific-sourced moisture
brings 40-80% Day 1 snow probs for >6" to these areas.

A shortwave trough digging down British Columbia as it rounds a
low over northern Alberta is the leading edge of the coldest
air-mass of the winter season to date, reaching into the interior
Northwest starting tonight and spreading across the Great Plains
through Saturday. Northwesterly flow off the coast of British
Columbia will strengthen as Alberta low and an expansive ridge
extending north through Alaska funnel Pacific moisture into the
Northwest and up the Columbia River Gorge today. With a strong
dome of Arctic high pressure (possibly approaching record high
pressure observations for the time of year in southwest Canada), a
plume of moisture running into the boundary, and the added help of
strong topographic ascent along ranges oriented orthogonally to
the mean flow, heavy snow mountain snow is expected to develop
across the southern WA through the OR Cascades into the northern
Rockies today with snow levels generally 2000ft or less. Day 1 WPC
PWPF shows high chances (>70%) for >12" of snowfall in the OR
Cascades and Blue Mountains and moderate (around 50% for the ID
Bitterroots to the Sawtooth. This focus shifts south through
Friday before being reinforced by a ridge cutting shortwave trough
that reaches the OR coast on Saturday with Day 2 probs expanded to
even larger areas of the OR Cascades, Sawtooth and the Wasatch.

A vorticity maximum shearing off from a long wave trough over the
northeast Pacific will develop an area of low pressure that tracks
towards Oregon coast Saturday morning. This wave will direct an
atmospheric river to far southern OR through far northern CA
Friday night with IVT values topping the 97.5 climatological
percentile. With cold initial conditions from the Arctic air
spreading south, heavy snow is expected at the onset with snow
levels in northern CA initially around 3000ft before rising to
5500ft on Saturday. Day 3 PWPF for >8" is 50-80% over the OR
Cascades, down the Sierra Nevada, across the ranges of the
northern Great basin, the Wasatch, and the western CO Rockies. The
warming onshore flow on Saturday looks to also cause a wintry mix
over west-central OR where a glaze of ice is possible. Day 3 PWPF
for >0.25" are 30-40% over the southern Willamette Valley west
into the Coast Ranges.

Jackson

***Key Messages for Jan 11-14 Major Winter Storm over the Midwest***

-High Confidence in Major Midwest Snowstorm
Heavy snow is expected in the Midwest with a powerful winter
storm. The greatest confidence in heavy snow exists in southern
and eastern Wisconsin, and western and northern Lower Michigan,
where over 12 inches of snow is likely (60-80%), causing
considerable disruption.

-Blizzard Conditions Possible with Strong Winds
Strong winds will spread into the Midwest and Great Lakes on
Friday and Saturday with the unusually powerful low pressure
system. This will make blizzard conditions possible, particularly
in exposed areas. Winds will increase on Friday night and the
drastically reduced visibility will make travel dangerous to
impossible. Wind gusts of 40 to 50 MPH may also lead to some power
outages.

-Lake Effect Snow Persists This Weekend
While the larger area of snow will begin to diminish on Saturday,
the arrival of colder air will generate heavy snow downwind of the
Great Lakes this weekend. Winds will remain strong, posing a risk
for significant blowing snow.

-Flooding and Severe Storms in the South and East
Severe thunderstorms will be possible Thursday and Friday in the
Gulf Coast and Southeast. Another round of rain in the
Mid-Atlantic and Northeast will lead to renewed rises on rivers
and streams and possibly flooding. Moderate coastal flooding is
also likely in the Mid-Atlantic and Northeast.

***Key Messages for mid-January Arctic Blast***

-Bitter Cold Surges South and Affects Most of U.S.
The first significant Arctic outbreak of the winter will arrive in
the northern Rockies and northern Plains Thursday night and
Friday, before advancing farther south and east through much of
the Plains and Midwest this weekend. Numerous daily cold records
are likely in the south-central U.S. on Sunday, Monday, and
Tuesday.

-Dangerously Cold Wind Chills Expected
At the peak of the Arctic outbreak early next week, minimum wind
chills should fall below zero into Texas and the interior
Southeast. Wind chills this weekend across the northern Plains and
northern Rockies should be below negative 30 degrees. This will
pose an increased risk of frostbite on exposed skin and
hypothermia. Have a cold survival kit if you must travel.

-Heavy Snow in the West Friday and Saturday
Arctic air will gradually lower snow levels in time for the
arrival of another storm system in the West on Friday. This may
lead to snow and considerable impacts in valleys in Oregon, Idaho,
Nevada, and Utah, including the Portland, Boise, and Salt Lake
City metro areas. Freezing rain is likely Saturday in western
Oregon.

-Southern, Northeast Snow Early Next Week
Snow is likely on the periphery of the advancing Arctic air mass
from the interior South into the Mid-Atlantic Sunday into Monday
and possibly over the Northeast into midweek. Stay tuned for
further details.
$$
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FOUS11 KWBC 120925
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 AM EST Fri Jan 12 2024

Valid 12Z Fri Jan 12 2024 - 12Z Mon Jan 15 2024

...Central Plains to the Great Lakes and Interior Northeast...
Days 1-3...

A soon-to-be negatively-tilted trough axis over North Texas early
this morning will continue to rapidly develop as it turns
northeast over MO today, reaching southern Lake Michigan by this
evening. Complimentary jet become S-shaped across the Great Lakes
will drive strong upper level divergence and robust surface
cyclogenesis with a deepening area of low pressure lifting from
the Ozarks early this morning to the L.P. of MI tonight. A swath
of heavy snow from eastern Neb through IA into northern IL will
continue to slowly pivot northeast downstream of the low, lifting
over WI and MI through tonight. As the low tracks northeast to
Quebec on Saturday, intense lake-effect snow will develop,
covering all five Great Lakes by Saturday night which continues
into midweek.

A wintry mix in the rain to snow transition zone through the WAA
precip continues this morning in a stripe over northern IL before
the system becomes dominated by just a rain-snow delineation.
North in the snow zone, significant snowfall is expected on the
northwest side of the low as a deformation band forms and slowly
pivots across the area, coincident with an intense TROWAL as the
WCB wraps into the low with a deep DGZ. The areas of greatest snow
potential (15-20 inches) remain eastern WI where the pivoting band
has lake enhancement which is also present over northeast portions
of the L.P. and in the Huron Mtns of the U.P. where lake
enhancement turns into lake effect snow. The powerful cyclone
reaches peak intensity over the L.P. tonight with MSLP in the low
to mid 970s making for very strong winds and likely blizzard
conditions north and then west of the low.

Day 1 WPC probabilities for at least 12 inches after 12Z are
greater than 50% over southern and eastern WI, northeastern
portions of the L.P. and the Huron Mtns in the U.P. which is the
favored snow belt favored in N-NW flow. There, strong northwest to
eventually west flow on the back side of the low envelopes all of
the Great Lakes with LES beginning off Lake Superior Saturday and
the rest of the Great Lakes by late Saturday night and continuing
in earnest through at least Sunday night with LES persisting over
all the lakes into Wednesday. Day 2 snow probs for more than 8
inches are over 50% for typical NW and W snow belts in the U.P.
including the Porcupine Mtns and 20-40% along the western shore of
MI, around Buffalo, and the Tug Hill. The powerful wind should
fracture dendrites which should limit max SLRs despite the deep,
saturated DGZ. Day 3 snow probs for more than 6 inches are high
around Buffalo and on the Tug Hill with some additional values in
the eastern U.P. Westerly flow LES then continues trough
Tuesday/possibly Wednesday.

On the eastern side of the approaching front, cold air mass in
place over the interior Northeast will slowly be eroded as broad
southerly flow scours out sub-freezing temperatures. The uneven
erosion in the column will likely lead to a period of snow to
freezing rain to rain in most areas of eastern NY and interior New
England outside northern Maine as a triple point low moves across
the area. Before the changeover, several inches of snow will
likely accumulate over terrain in interior portions of the
Northeast with Day 1.5 WPC snow probabilities for more than 6
inches highest (generally >70%) over the Adirondacks, Green &
White Mtns, and interior Maine (North Woods).

...The West...
Days 1-3...

An active wintry pattern will continue throughout much of the
mountain ranges along the West Coast, much of the Great Basin to
the Colorado Rockies through this weekend across the boundary of
Arctic cold air over this region. A shortwave trough pushing into
WA from BC is rounding a deep low centered over Alberta and send a
surge of potently cold air over the Northwest today before
stalling over southern OR where it will persist through this
weekend. A rich plume of 850-700mb moisture running along this
boundary, along with topographic lift will allow heavy snow to
continue over the OR Cascades, across southern ID, northern UT and
the Wasatch, to the CO Rockies today. Day 1 PWPF for >8" are high
(over 90%) along the OR Cascades and the Wasatch and moderate
(40-70%) over southern ID into northern NV. Strong winds are
expected in this tight baroclinic zone with blizzard warnings up
in southern ID.

Meanwhile a compact southern stream low cuts through the North
Pacific/Alaska ridge tonight, reaching the OR Coast late Saturday.
This storm system will tap into a conveyor belt of moisture that
has origins into the subtropics. The combination of anomalous
moisture and a strong 850mb jet will lead to IVT values
approaching the 99th climatological percentile being directed at
southern Oregon and northern California. This brings further heavy
snowfall in the Oregon Cascades with the footprint expanding south
through the Sierra Nevada. Confidence is highest in heavy snowfall accumulations along the stationary front from southern Oregon and
northern Nevada to the Wasatch which is at the nose of the strong
IVT plume emanating out from the northeast Pacific. Day 2 WPC PWPF
sports high chances (>80%) for more than 8 inches of snowfall over
the OR Cascades/Trinity Alps/Sierra Nevada east through the
northern Great Basin ranges, the Wasatch and the CO Rockies.

As this wave comes ashore, warm air riding over the Arctic air at
the surface sets up a significant freezing rain case for northwest
OR into southwest WA. Day 2 PWPF for more than 0.25 inches of ice
area 30 to 60% over much of the Willamette Valley south of
Portland west through the Coastal Ranges.

Ridging begins to shift east into The West Sunday, with precip
shifting east. Day 3 PWPF for more than 8 inches is moderately
high (50-80%) over the Wasatch and CO Rockies south through the
NBM border in the San Juans. All told, three day totals of over 4
feet are expected on the highest OR Cascades and Wasatch with 2
feet or so for the Sierra Nevada and CO Rockies. Also noteworthy
are low probabilities for more than two inches over the Portland
metro on both Days 1 and 2.

...Mid-South...
Day 3...

The southern stream shortwave trough that slices through the North Pacific/Alaska ridge tonight crosses the southern Rockies Sunday
and rounds the base of the expansive trough over the central part
of North America Sunday night. Gulf moisture is available to ridge
up and over the cold front that pushes through Texas and well into
the Gulf, allowing precip to break out over North Texas/OK before
crossing AR into TN and northern MS/AL. Sufficient cold air in
this Arctic airmass allows moisture in the DGZ with SLRs in the
mid to upper teens. There remains uncertainty with the
strength/timing of this wave/reinforcing waves with the 00Z ECMWF
stepping back its QPF footprint over the area, but for now the Day
3 snow probs for >4" are 10 to 40% from OK across northern AR well
into western TN. Given the strength of the jet under this trough
and the particularly cold air, having accumulating snow over this
area is a good bet, so stay tuned for further updates.

Jackson


***Key Messages for Jan 10-14 Major Winter Storm over the Midwest***

--Conditions Deteriorate Rapidly Today in Midwest
Heavy snow will continue to spread across the Upper Midwest today.
Snowfall rates of 1 to locally 2 inches per hour will lead to
hazardous travel conditions over much of the region

--Blizzard Conditions Likely with Strong Winds
Winds will increase through tonight in the Midwest and Great Lakes
as the storm system rapidly strengthens. Blizzard conditions are
likely, particularly in exposed areas. Travel will become
dangerous to impossible with whiteout conditions. Power outages
are possible.

--Lake Effect Snow Persists This Weekend
While the larger snow area will diminish on Saturday, the arrival
of colder air will generate heavy, wind-driven snow downwind of
the Great Lakes this weekend into midweek. Whiteout conditions in
the blowing lake effect snow are expected in the stronger lake
effect snow bands.

--Flooding and Severe Storms in the South and East
Severe storms will be possible in the South today and damaging
gusts may occur outside of thunderstorms. Heavy rain in the
Mid-Atlantic and Northeast tonight and Saturday will lead to
renewed rises on rivers and streams and possible flooding.
Moderate coastal flooding is likely in the Mid-Atlantic and
Northeast Saturday, with significant impacts. Major coastal
flooding is possible in New Hampshire and Maine.


***Key Messages for mid-January Arctic Blast***

--Bitter Cold Surges South and Affects Most of U.S.
The first significant Arctic outbreak of the winter arrives into
the Northwest, the northern Rockies, and northern Plains today,
before advancing farther south and east this weekend and early
next week. Numerous daily cold records are likely.

--Dangerously Cold Wind Chills Expected
Sub-zero wind chills will affect much of the U.S. and reach into
portions of the South. Wind chills this weekend across the
northern Plains and northern Rockies will be below negative 30
degrees on a widespread basis, and as cold as negative 50 to 60
degrees on Saturday morning in Montana and the western Dakotas.
This will pose an increased risk of frostbite on exposed skin and
hypothermia. Have a cold survival kit if you must travel.

--Heavy Snow in the West Today and Saturday
Arctic air will gradually lower snow levels in time for the
arrival of another storm system in the West today. This will lead
to snow and considerable impacts in valleys in Oregon, Idaho,
Nevada, and Utah, including the Portland, Boise, and Salt Lake
City metro areas. Significant freezing rain is likely Saturday in
northwestern Oregon.

--Additional Wintry Precipitation Early Next Week
Areas of snow, sleet, and freezing rain are likely on the
periphery of the advancing Arctic air mass from the interior South
into the Northeast. Stay tuned for further details as the forecast
may change.
$$
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