FXUS65 KCYS 111742

Area Forecast Discussion
National Weather Service Cheyenne WY
1042 AM MST Mon Dec 11 2023


Issued at 225 AM MST Mon Dec 11 2023

With gusty winds across the wind prone areas continuing to
diminish early this morning, main forecast concern over the next
48 hours will transition to the potential for snow, fog, and
some freezing drizzle across the region as the next Pacific
storm system moving into the Pacific Northwest digs southeast
into the northern Great Basin region today. Further north, IR
Satellite loop and surface observations show a fast moving polar
cold front pushing south into Montana and the Dakotas early this
morning. This front is expected to already be on our doorstep by
noon today with surface winds shifting into the north through
the afternoon. The lift associated with the cold front, low
level moist upslope flow, and some midlevel forcing associated
with the poorly organized Pacific trough will combine to give
southeast Wyoming and portions of western Nebraska a 6 to 12
hour window of light snow and some frozen precipitation starting
late this (Monday) afternoon through Tuesday morning. High
temperatures today will likely occur around noon before the
colder airmass pushes south into the region, with readings in
the 40s. Temperatures will likely lower into the upper 20s to
mid 30s quickly by late this afternoon.

Although forcing with this system will generally be weak, NAEFS
low level analysis shows a local maximum of high moisture
content and localized moisture convergence across far southeast
Wyoming and the southern half of the Nebraska Panhandle. In
fact, PW's are closer to the 90th to 95th percentile of December
climatology...which tends to be a dry month around here. This
is pretty impressive and is a little concerning with forced
upslope along and east of the Laramie Range. With that said, the
system is poorly organized and doesn't stick around for too
long as models show most of the precipitation ending by late
Tuesday morning or early in the afternoon. Model Omega has been
steady and showing around 5 to 8 hours of decent lift around
700mb with a good chance for light to occasionally moderate snow
with snowfall rates of one eighth to one quarter of an inch per
hour. This should roughly translate to snow accumulations of
around 1 inch across the area with a few places around Goshen,
Platte, and Laramie County receiving somewhat higher accumulations
but nothing more than a few inches. Since the upper level trough
is so poorly organized and digs south west of Wyoming, expect
some drier air aloft to move into the region starting early
Tuesday morning. Model soundings are showing a dry airmass just
above 750mb with a shallow moist layer towards the surface.
There will still be some lift in the area during the time due to
upslope flow, so expect a period of fog and freezing drizzle
from early Tuesday morning through noon Tuesday which may impact
the rush hour. Otherwise, snow and ice accumulations are still
expected to be below Winter Weather Advisory criteria so may
issue a Special Weather Statement for the area to cover the
threat of ice and snow.

For the mountains, not planning any headlines at this time
after a quick look at the SNOTEL data across the higher
mountain ranges. Snow accumulations with each impulse over the
past three days have generally been between 2 to 5 inches.
Another lull in the activity is expected this morning, with snow
picking up in intensity this afternoon. However, expect an
additional 2 to 4 inches with this next system, if that, since
the cold front may not make it too far west. One place to watch
for is the Interstate 80 Summit between Cheyenne and Laramie
where the best lift will be location through the duration of the
event. May see winter weather advisory criteria for 3 or 4
inches of snow and some ice accumulation due to freezing

By Tuesday evening and Tuesday night, weak storm system digs
south into the southern Great Basin Region with snow ending
across southeast Wyoming and western Nebraska. Skies will remain
mostly cloudy with near average low temperatures in the teens to
low 20s.


Issued at 230 AM MST Mon Dec 11 2023

Pretty benign conditions in the long term as all the weather
will be south of Wyoming with a low pressure system tracking
across southern Arizona and New Mexico. This leaves southeast
WYoming and Nebraska Panhandle in weak flow aloft and mainly
sunny skies/dry weather.

Upper low tracks into western Texas Thursday night/Friday
morning with a weak upper ridge of high pressure slowly building
into our CWA. May start to get back into northwest flow Friday
afternoon as an upper shortwave tracks across Montana.

Could see an increase in winds Saturday as gradients begin to
increase once again. Marginal high wind event possible in the
wind prone areas Saturday night into Sunday morning as gradients
increase...but given that is six to seven days out...confidence
is low to really change any wind guidance at this time.


Issued at 1039 AM MST Mon Dec 11 2023

A cold front will bring deteriorating flight conditions
throughout the afternoon and overnight to southeast Wyoming and
western Nebraska terminals. Snow showers will develop across
southeast Wyoming terminals this afternoon and evening. Expect
low CIGs and poor visibility in falling snow. IFR/LIFR
conditions are likely tonight through tomorrow morning. Snow
will arrive later tonight and early Tuesday morning at western
Nebraska terminals. Expect similar conditions with low CIGs and
poor visibility in falling snow. Freezing drizzle could also be
possible at KCYS Tuesday morning.