Quantitative Precipitation Forecast
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FOUS11 KWBC 221932
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 PM EDT Fri Mar 22 2024

Valid 00Z Sat Mar 23 2024 - 00Z Tue Mar 26 2024

...Northeast...
Day 1...

Shortwave energy moving through the base of a broad northern stream
trough will support a sharpening baroclinic zone that will slide
east from the eastern Great Lakes overnight.  Amplifying low level
flow will support increasing moisture advection into an area of
large-scale ascent affording in part my right-entrance region upper
jet forcing. Precipitation will blossom across much of the Northeast
by daybreak, with heavy wet snow is likely to develop initially
across portions of the Adirondacks into the Green and White
Mountains Friday night into Saturday morning.

Meanwhile, an icy transition zone is likely form to the south along
New York`s Southern Tier through the mid Hudson Valley.  Heavy snow
will continue to spread further east across during the day,
stretching across interior Maine during the late morning hours.

As the northern and southern stream begin to interact, a coastal low
will track along the Mid Atlantic coast -- directing warm air
further north that will support rain across southern New England and
an any icy transition zone that will shift north from central into
northern New England.  Some areas, especially across interior
northern New England may return to snow before precipitation ends as
the low tracks into Atlantic Canada and the front slides offshore
late Saturday.

The latest WPC PWPF shows high probabilities (greater than 70
percent) for snow accumulations of 8 inches or more extending from
the Adirondacks through most of interior Maine.  The WSSI indicates
moderate to major impacts extending across much of the same area.
Moderate probabilities (40 percent or greater) for ice
accumulations of 0.10 inch or more stretch from the Catskills to
along portions of coastal Maine.


...Pacific Mountain Ranges...
Days 1-3...

A strong, large closed upper level low positioned just off the West
Coast this afternoon will push a plume of higher moisture into the
Pacific Northwest tonight/Saturday, bringing heavy mountain snow to
the region. IVT values reach 400 kg/m/s through tonight and this
should produce heavy snow for the northern CA ranges initially then
into the Sierra Nevada late tonight/Saturday.

Snow levels will initially start out between 4,000-5,000ft tonight
but drop to as low as 3,000ft by Saturday as the upper low moves
into the Pacific Northwest. However, snow totals that likely
surpass 12" will be at elevations >5,000ft Saturday and through
Sunday morning. Farther north, while the moisture transport is not
as pronounced, the Pacific Northwest lies directly ahead of the
approaching upper low, which still supports prolonged synoptically-
forced ascent aloft to go along with falling snow levels. Snow
levels will be a near carbon-copy of the scenario farther south in
the California Ranges with the Cascade Range and Olympics >5,000ft
having the better odds of seeing cumulative snowfall totals through
Sunday topping 12". As the upper low moves ashore and over the
Northwest on Saturday, the axis of Pacific moisture will be
oriented farther inland and lead to periods of heavy mountain snow
for elevations >6,000ft in the Great Basin, the Blue Mountains of
eastern Oregon, the Bitterroots, Tetons, Absaroka, and as far
inland as the Wasatch and Colorado Rockies by Saturday night.

WPC snow probabilities are high (>70%) for at least 12 inches of
snowfall for the event across the Sierra Nevada and the
Salmon/Siskiyou/Trinity mountains. For the higher elevations,
generally above 7500-8000 ft, there are moderate/high probabilities
for at least 18 inches. Once the snowfall threshold dips to >6",
the Olympics and Cascades, as well as the Absaroka, Tetons, and
portions of the western Colorado Rockies sport moderate-to-high
chances (50-70%) for those snowfall totals.

...Northern Rockies & High Plains, Central Rockies, Upper
Midwest...
Days 1-3...

**Major Winter Storm Set to Impact Northern/Central Rockies to
 Upper Midwest Beginning This Weekend**

The combination of lower pressure over the West/Intermountain West
and sprawling high pressure over the Canadian Prairies will bring
a long duration easterly flow regime to the Intermountain
West/Northern Rockies through tomorrow. Aloft, a jet streak
positioned over the Dakotas will put the region in the favored
right entrance region of the 110 kt jet while heights will begin to
lower with the approaching shortwave energy. This is a recipe for
periods of snow through tomorrow for the western Montana Rockies
as well as central Montana and further south into the Absaroka and
Big Horns. Accumulations should be fairly minor with only the Big
Horns seeing any substantial probabilities for greater than 4
inches.

For Day 2 (Saturday evening/Sunday), a stronger shortwave trough
rounds the base of the larger trough over the Four Corners/Rockies
regions and this will kick off a strengthening low pressure in the
lee of the Rockies. Moisture anomalies increase significantly,
reaching well north into the Northern Plains, wrapping around the
northern flank of the strengthening surface low. All around,
favorable forcing for ascent provided by the falling heights,
deepening low pressure, and left exit region dynamics from a strong
jet streak over the S. Plains. This will bring a shield of heavy
precipitation from the Four Corners region including the Colorado
Rockies, northward into the Northern Rockies then along the WAA
wing into Minnesota and western Wisconsin. For Day 2, the WPC snow
probabilities are high for 6" across western CO Rockies and are in
the moderate to high range (40-70%) across much of central/eastern
MT through central MN and far west-central WI.

For Day 3 (Sunday evening/Monday), the low pressure deepens more
and lifts to the northeast, reaching the MN/IA border by 00Z Tue. A
classic setup for long duration snowfall north/northwest of the 700
mb low sets up with a favorable TROWAL signature. Moisture
anomalies are very impressive, with a strong tap into the Gulf of
Mexico moisture. QPF probabilities for 1"+ in the 24-hr period are
moderate/high from north-central NE through southeast SD and
southwest to central MN. A tricky thermal/ptype forecast as a sharp
rain/snow (maybe embedded mix transition zone) and trends in
guidance have lifted the zone of greatest snow to the north some.
Some waffling in the track/thermals expected over the next couple
of days. 8 inch snow probabilities are high (>70%) for a large area
from northern NE through MN for Day 3 and are solidly in the
moderate range (40-60%) for 12 inches. 3-day totals may reach 18-24
inches across portions of eastern SD through central MN. This will
bring a significant/major winter storm to the region where the
combination of snow amounts, snow load, and blowing snow/winds will
create disruptive and significant travel impacts. The WSSI-P
highlights a near 100% probability for Moderate Impacts across
portions of the region and for Major Impacts, the probabilities
reach 30-40%.

Taylor/Peireia/Mullinax

***Key Messages for Northern Plains Winter Storm***

--Significant winter storm likely

There is high confidence that an extensive storm system will
produce widespread heavy snow and gusty winds over the Northern
Plains into the Upper Midwest.

--Widespread heavy snow expected

Heavy snow will likely spread across much of central and eastern
Montana by Saturday night, then expand into the Northern Plains and
Upper Midwest on Sunday. There is a high chance (>70%) of at least
eight inches of snow extending from portions of the Dakotas and
north-central Nebraska northeastward through Minnesota into
northern Wisconsin.

--Hazardous impacts due to snow, snow load, and wind

A combination of heavy snow and gusty winds will likely produce
areas of blowing and drifting snow, as well as possible blizzard
conditions Sunday into Monday. Hazardous travel, along with some
disruptions and closures are expected late Saturday into Monday.
The combination of strong winds and heavy, wet snow on trees and
power lines may result in tree damage and power outages.

--Additional forecast changes anticipated

Uncertainty remains with precipitation type for southern-most
areas and a possible sharp northern snowfall gradient in northern-
most areas. Closely monitor the latest forecasts as the storm
evolved over the next 24-48 hours.


$$


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