Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Thu Feb 08 2024

Valid 12Z Thu Feb 08 2024 - 12Z Sun Feb 11 2024

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

A vigorous upper level vort max tracking through the Desert
Southwest this morning will once again bring another surge in
850-500mb moisture over the Four Corners region today and into
Thursday night. Strong upslope flow via southwesterly 850-500mb
winds, large scale lift courtesy of 500mb PVA aloft, and a
divergent left-exit region from a 150kt 250mb jet streak overhead
will help maximize strong vertical velocities at mid-upper levels
of the atmosphere through early Friday morning. WPC PWPF shows
high chances (>70%) for snowfall >12" along the Mogollon Rim where
elevations are >7,000ft and in the San Juans whose elevations are
>9,000ft. Similar high probabilities for >8" exist in the higher
terrain of the Wasatch, near Zion National Park in southern Utah
and many of the >9,000ft ranges of west-central Colorado. The WSSI
continues to depict Moderate impacts in these aforementioned
ranges through early Friday morning with some embedded Major
Impacts along the Mogollon Rim and near Zion National Park.

Farther north, the Cascade Range will witness a period of lighter
snowfall today as an upper level disturbance meanders its way over
Washington. Snow will pick up in intensity late Thursday into
Friday morning as a more potent vort max dives southeastward from
British Columbia. The nose of a 130kt 250mb jet streak and a
resurgence of 850-700mb moisture flux being directed at the
Pacific Northwest via northwesterly flow will spur periods of
heavy snow along the Cascade Range and even as far inland as
Oregon's Blue Mountains. WPC PWPF shows high chances (>70%) for
>4" of snowfall on Thursday and into early Friday morning. Similar
probabilities for >4" of snow are depicted across the Blue
mountains of northeast Oregon late Thursday through Friday
morning. The upper trough over the Northwest and a frontal
boundary drifting south will still support periods of heavy snow
in the tallest peaks of the Lewis Range of western Montana. Latest
WPC PWPF shows moderate-to-high chances (40-70%) for >8" of snow
in these ranges Thursday evening and into the day on Friday.

By Friday afternoon, the upper level shortwave trough over the
Northwest will continue to dig south into the Southwest where it
will eventually become a 500mb low over northern Arizona early
Saturday morning. The resulting 500mb height falls, PVA over the
Four Corners region, and added influx of 700-500mb moisture will
give rise to more snow along the Mogollon Rim, the Gila Mountains,
and portions of the Wasatch. WPC PWPF shows moderate chances
(40-60%) for >6" of snow in parts of these ranges Friday night
into the day on Saturday.

...Eastern Montana & Western North Dakota...
Days 1-2...

The strengthening surface low will over eastern North Dakota is
causing winds within the 850-700mb layer that were originally out
of the SE to flip more out of the NE-ENE. This allowed the
atmospheric column to cool below freezing and allow for snow to
become the primary precipitation type. Snow will fall heavily at
times in eastern Montana and western North Dakota where hourly
snowfall rates could approach 1"/hr at times this morning. As the
storm continues to track northeast and the best forcing tracks
north, snow rates will gradually taper off late Thursday morning
but occasionally gusty winds will persist as well. While not
extreme by northern High Plains standards, this may still
contribute to reduced visibilities and drifting snow on roads. The
storm will lift into northern Minnesota by Thursday afternoon with
snow falling across central North Dakota and northern South
Dakota. Snow is possible across the Red River of the North
Thursday night and into northern Minnesota by early Friday
morning. Snow should finally come to an end by Friday afternoon as
the storm tracks northeast into the heart of Ontario. WPC PWPF
sports low-to-moderate chances (20-50%) for additional snowfall
totals >4" in parts of eastern Montana with low chance
probabilities (10-30%) in northern North Dakota. The WSSI shows
primarily Minor Impacts from eastern Montana on east to the Red
River of the North with some pockets of Moderate Impacts in some
portions of northeast North Dakota. These impacts are depicted
generally due to a combination of the Snow Amount and Blowing Snow
algorithms.

...Central Rockies & Central High Plains...
Days 2-3...

The amplifying upper low in the Southwest and a weak 500mb
disturbance tracking through Wyoming will spawn a strengthening
surface trough in lee of the Rockies over eastern Colorado Friday
night. Farther south, the best PVA will be directed over eastern
New Mexico and the Texas/Oklahoma Panhandles, eventually causing
the formation of a surface low east of Roswell Saturday morning.
As high pressure builds in over the Northwest, the tightening
pressure gradient will lead to an acceleration in E-SE 850mb winds
over the Central Plains that advect 850mb moisture flux towards
the Front Range of the Colorado Rockies and as far south as the
Sangre De Cristo Saturday morning. Meanwhile, as the upper trough
over the Southwest approaches during the day, it will deliver
700mb moisture flux into the region as well. As Saturday unfolds,
both the GEFS and EPS show a 700mb low forming somewhere over
northeast New Mexico by late afternoon. To the north of this low
is where low-level moisture is most likely to wrap around the
northern and western flank of the 700mb low and provide the best
opportunity for heavy snowfall starting as early as midday
Saturday and lasting into Sunday morning.

Latest WSO has shown in increase of probabilities for snowfall
exceeding warning criteria over southeast Colorado, northeast New
Mexico, and the western Texas/Oklahoma Panhandles. This is due to
ensemble members keying in on the potential for banding on the
northwest periphery of the 700mb low track into areas such as
Raton Pass. Farther north towards the Palmer Divide and the Denver
metro area, it is more a function of duration as the initial
upslope flow Friday night lingers through Saturday evening, making
snowfall rates not as impressive, but more of a prolonged 18-24
hour long event that eventually allows snow totals to top 6" in
areas east of the Front Range. The latest WPC PWPF does show
moderate-to-high chances (40-70%) or snowfall totals >6" with the
Palmer Divide seeing the higher end of those listed probabilities.
Probabilities are also in the moderate to high range (50-80%)
along the Sangre De Cristo in southern Colorado and far northern
New Mexico. This is an area that also sports some notably high
outlier (90th percentile) outcomes given their closer proximity to
the 700mb low. Far southeast Colorado and far northwest New Mexico
also sports moderate-to-high probabilities (50-70%) as well
through Saturday night. The forecast remains fluid with additional
changes possible (largely due to the uncertainty in where the
700mb low forms) but the setup is one that has resulted in heavy
snow in portions of the High Plains of New Mexico and Colorado
before, and can even produce heavy snow as far east as both the
Texas/Oklahoma Panhandles and southwest Kansas based on the 700mb
low track. Those with interest in these areas should monitor the
forecast closely over the next 24-72 hours.

Mullinax