115
FXUS65 KRIW 222203
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
303 PM MST Fri Nov 22 2024

.KEY MESSAGES...

- One more day of mild autumn temperatures, but change on the
  horizon.

- Next trough still expected for this weekend, ushering in a
  return to colder, yet normal autumn temperatures.

- Modest snowfall expected for all higher elevations of west and
  central WY through Sunday night, along with some light
  accumulations for Sweetwater and Natrona Counties.

&&

.DISCUSSION...
Issued at 135 PM MST Fri Nov 22 2024

High cirrus continue to spread across western WY today, pouring
in from off the California coast. This is wrapping around the
generally idle trough just off the Washington state coast. As
this system pulls apart, the energy will start ejecting across
the Northern Rockies during the next 24 hours. The main portion
will impact WY over the weekend, starting across the western
mountains during Saturday and Saturday night. This will have
enough of a moisture tap from the Pacific to bring some
snowfall, mainly to the higher elevations. The Tetons have a
better than 50% chance for 6 inches, but chances for a full 12
inches remain under 10%. As this first system sweeps east, the
generally pattern remains from the southwest off the Pacific,
while more pieces of the Pacific trough detach and sweep east.
Another piece follows behind Saturday night, bringing a chance
for snowfall for southern WY, spreading into Natrona County
Sunday morning. Currently accumulation forecast remains below an
inch for the greater Casper area, and 1 to 2 inches along and
south of I-80 in Sweetwater County.

The system Saturday night will help get colder air back across
the state, with highs Sunday a good 10 to 15 degrees lower than
Saturday, struggling into the 30s. The cold pool will anchor
sufficiently west of the Divide next week, with highs only in
the 20s, and lows right around zero. East of the Divide, a brief
warm-up into the lows 40s on Tuesday, but this will be short-
lived as the rest of the Pacific trough finally moves southeast,
opening up northwest flow out of Canada, reinforcing the colder
air across the state. Right now, the coldest plunge then looks
to deflect east into the Northern Plains, so highs remain in the
20s and 30s for the time being.

Until the trough finally drops through later Wednesday, the
precip patter remains unsettled, with moisture continuing from
the Pacific to bring light snow, but this will likely be limited
to higher elevations, with lower elevations seeing minimal travel
impact for the busiest travel day of the year.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 259 PM MST Fri Nov 22 2024

VFR conditions prevail through the evening, with relatively
light winds and high clouds prevailing. Winds increase in the
upper and mid levels overnight ahead of the next weather system,
leading to LLWS at CPR and perhaps COD. There is a chance (30%)
that gusts could continue to reach the surface overnight, which
would eliminate shear.

After sunrise Saturday and into the late morning, winds will
mix down to the surface. Strong wind gusts in the 30 to 40 kt
range are likely for many locations by mid afternoon. Increasing
mid-level clouds move in Saturday afternoon. Snow develops west
of the Continental Divide Saturday evening and into the
overnight hours, which will reduce visibility at locations such
as JAC.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Straub
AVIATION...VandenBoogart