179
FXUS65 KRIW 221037
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
337 AM MST Fri Nov 22 2024

.KEY MESSAGES...

- A few snow showers in northwestern Wyoming, remaining dry and
  mild east of the Divide.

- A Pacific system will bring some snow Saturday and Sunday,
  with the highest amounts in the northwestern mountains.

- Seasonable and unsettled weather continues into next week.

&&

.DISCUSSION...
Issued at 232 AM MST Fri Nov 22 2024

Things look to be turning more active over the next week or so. At
this time, a weak shortwave is passing over northwestern Wyoming
with some snow showers, mainly in the mountains. Moisture is not
that deep with this initial system, so any accumulations will
be lighter. Most should end in the early afternoon and then
there should be around a 12 to 18 hour period of mainly dry
weather. Meanwhile, areas east of the Divide should have a nice
late fall day with a continuation of above normal temperatures.
There will be a gusty wind near Casper, but wind should be
somewhat less than recent days as shortwave ridging passes over
the area.

A somewhat more potent system, a piece of the intense low off of the
Pacific coast, will move toward the area following this. Guidance
has slowed down the arrival of the system, with dry weather expected
through sunrise Saturday and the steadier precipitation holding off
until the afternoon. At this point, this does not look like a major
storm. Most guidance shows the system splitting, limiting amounts
somewhat. Through most of Saturday night, precipitation should be
largely restricted to areas west of the Divide. Things may
change a bit on Sunday as the trough moves through. Some
guidance is showing some snow showing up roughly from Sweetwater
County toward Casper with some energy from a jet streak moving
overhead. As for amounts, the highest amounts will likely fall
over the usual suspects, mainly the Tetons and southwestern
Yellowstone Park, where there is anywhere from a 1 in 2 to a 4
out of 5 chance of 6 inches or more. The chance of over a foot
is less than 1 out of 4 though. As for the western valleys, the
chance for 4 inches or more is no more than 1 out of 5. The
precipitation may even start as rain in the valleys with 700
millibar temperatures between minus 2C and minus 4C initially
that could put snow levels from 6500 to 7500 feet. Any potential
highlights would more than likely be advisories and probably
restricted the northwestern mountains. Sweetwater County has a
around a 1 out of 2 chance of an inch or more. Casper has a
small chance, but this is higher than before and amounts may
rise if this trend continues. As for other details, areas east
of the Divide will have a dry and mild day on Saturday. The main
concern on Saturday here will be another day of increased wind
around Casper, with probabilistic guidance showing a 1 out of 2
chance of wind gusts of 40 mph or more. The chance of gusts to
60 mph are low. So, no wind highlights are expected but
Saturday may be windy enough to cause a couple of problems with
high profile vehicles. Temperatures then fall back to near
normal levels behind the front on Sunday.

Shortwave ridging should then bring mainly dry weather for Monday.
The next potential weather maker then moves in for Tuesday into
Wednesday. Models have less agreement with this one with some
keeping the energy south and a few possibly having a brief
period of northerly upslope flow that could bring some snow
east of the Divide. An Alberta Clipper may then bring some light
snow for the end of next week. Temperatures will be cooler than
today and Saturday, but with the flow mainly zonal and Pacific,
temperatures will average near normal and not below normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 335 AM MST Fri Nov 22 2024

VFR conditions are expected to prevail at terminals through the
TAF period. Snow is now expected to stay well to the north of
the KJAC terminal, so have removed the PROB30 group from the
forecast. Light winds will also continue for most terminals,
except KCPR, where a gusty southwest wind occurs through the
afternoon hours.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...LaVoie/Myers