Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Fri Feb 09 2024

Valid 12Z Fri Feb 09 2024 - 12Z Mon Feb 12 2024

...The West... 
Days 1-2...

The nose of a 130kt 250mb jet streak and a resurgence of 850-700mb
moisture flux being directed at the Intermountain West via
northwesterly flow will spur periods of
heavy snow from Oregon's Blue Mountains on south and east into the
Great Basin, along the Wasatch, and as far east as the Absaroka
and Big Horns. WPC PWPF shows high chances (>70%) for >8" of
snowfall today along the Big Horns. Meanwhile, moderate chances
(40-60%) for >4" of snow are present in the Blue Mountains while
probabilities shoot up to high chances (>70%) in the peaks of the
Great Basin and along the Absaroka on Friday. 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
through Friday night.

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 by
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,
the spotty mountain ranges around Tuscon, and portions of the
Wasatch. WPC PWPF shows low-to-moderate chances (20-50%) for >6"
of snow in parts of these ranges Friday night into the day on
Saturday.

...Central and Southern Rockies into the Plains...
Days 1-3...

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 the Guadeloupe Mountains
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 within southwesterly flow into
the region as well. As Saturday unfolds, both the GEFS and EPS
show a 700mb low forming over central New Mexico Saturday
afternoon that tracks towards Lubbock, Texas by early Sunday
morning. 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 late afternoon Saturday and lasting through
Sunday morning.

Boundary layer temperatures are less in question along the Front
Range of the Rockies and High Plains of southeast Wyoming, through
central Colorado, and on south to the CO/NM border. Here, snow
will be the primary precipitation type and will have the benefit
of persistent upslope flow on the northern flank of the 500-700mb
layer-averaged low position. However, the recent trend south in
the 500mb low is resulting in winds at low levels not being quite
as strong as they will be farther south. From Cheyenne on south to
the Palmer Divide (the Denver metro area included in this area),
latest 48-hour WPC PWPF depicts low-to-moderate chances (30-60%)
for >6" of snow with tallest peaks along the Colorado Front Range
and a swath of northeast Colorado, western Nebraska, and southeast
Wyoming seeing odds closest to the 50-60% range. Farther south,
down near the Raton Mesa, this area may be most primed for heavy
snow given their closer proximity to the 500mb low. This area will
also be better aligned for maximizing upslope flow into the NM/CO
border. 48-hour WPC PWPF shows high chances (>70%) for >6" of
snowfall through Sunday morning, as well as low-to-moderate
chances (10-40%) for snowfall totals >12".

As the 500mb low matures south of Lubbock on Sunday, the
deformation axis will shift east into the OK/TX Panhandles. The
left-exit region of a 100kt 500mb jet streak (topping out around
the 99th climatological percentile over the Big Bend Sunday
morning) will be located over the Texas Panhandle and coincide
with southeasterly flow out ahead of the 500mb low that is tapping
into >90th climatological percentile PWs over North Texas. As the
warm conveyor belt wraps around the 700mb low and dynamic cooling
ensues aloft, any initial rainfall early Sunday morning will
switch over to snow over the Texas Panhandle and into west-central
Oklahoma. These deformation axes can produce exceptional snowfall
rates that could approach 1-2"/hr. In fact, WPC PWPF now sports
low-to-moderate chances (20-50%) for >12" of snowfall near and
along I-40 and between Amarillo and Lubbock, signifying members of
the WPC WSE do feature >12" snowfall amounts for the event.
Boundary layer temps become more in question over central Oklahoma
as there remains a great deal of uncertainty in how long and
strong the deformation axis can be. WPC PWPF sports
moderate-to-high chances (50-70%) for snowfall totals >6" over
portions of Texas Panhandle (between Amarillo and Lubbock, as well
as along the I-40 corridor) and the western-most portions of the
Oklahoma Panhandle. There are some guidance members that keep the
deformation axis in tact long enough to produce a swath of >4"
snowfall totals over central Oklahoma and southwest Missouri
Sunday afternoon and evening (WPC PWPF shows low-to-moderate
chances (20-40%) in central Oklahoma, low chances (10-30%) in
southwest Missouri). This is more unclear at this moment, but
trends in guidance will be closely monitored over the next 24-48
hours.

The probability of significant icing greater than 0.10" is less
than 10% for days 1-3.


Mullinax