594
FXUS65 KRIW 152256
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
356 PM MST Sat Nov 15 2025

.KEY MESSAGES...

- High confidence in high temperatures 15 to 20 degrees above
  normal today and Sunday with breezy winds.

- Rain and snow beginning Sunday afternoon across the west and
  spreading east of the Continental Divide early Monday. The
  greatest snow amounts are expected (80% chance) across the
  western mountains; however, the Green River Basin and western
  valleys could see a light dusting to 1 inch by Monday morning.

- Seasonal temperatures look favorable much of next week with
  multiple opportunities for precipitation.

&&

.UPDATE...
Issued at 107 PM MST Sat Nov 15 2025

20Z water vapor imagery shows the transitory ridge axis approaching
the southwest corner of Wyoming with strong northwesterly flow
aloft over Montana and the eastern half of Wyoming. Gusty 20 mph
to 25 mph winds are being observed across many locations east
of the Continental Divide, thanks to the strong flow aloft. As
the ridge axis traverses the state over the next 24 hours,
expect winds to decrease and cloud cover to increase. On the
west side of the axis, southwesterly flow aloft will usher rich
Pacific moisture into the state ahead of the forecasted upper
low ejecting into the region.

Precipitation chances have remained consistent in spreading
southwest to northeast as an associated 700 mb low treks across the
state late Sunday into Monday. Mean 700 mb temperatures behind the
low only drop to -2C to -4C by Monday morning. This reflects snow
levels generally around 6500 ft to 7500 ft, with the 6500 ft snow
levels west of the Divide. This favors a light dusting to an inch of
snow (50-80%) for locations across the Green River Basin early
Monday morning. The higher elevation western mountains have an 80-
90% chance of snow amounts of at least 6 inches by Monday morning
but drop to only around 50% for 10 inches across the highest peaks.
No highlights are expected at this time given the western mountain
passes have less than a 40% chance of at least 6 inches of snow by
Monday morning. As for those east of the Divide, precipitation is
still forecast to fall as rain with snow levels only dropping to
7500 ft when precipitation is expected. Monday is forecast to be a
wet one for most. Cooler and more seasonable temperatures are still
expected through the rest of the work week with various chances for
precipitation, particularly Wednesday into Thursday.&&

.DISCUSSION...
Issued at 104 AM MST Sat Nov 15 2025

We still have some gusty wind out there early this morning. These
should continue to decrease through the night though as the jet
streak moves away and ridging, although of the transitory kind,
builds back over Wyoming. This should result in a fairly nice start
to the weekend, with a mix of clouds and sun and another day of mild
temperatures, anywhere from 10 to 20 degrees above normal. With the
radar largely quiet, we have removed the POPs for this morning.
There will still be some breezy conditions around Casper today, but
with 700 millibar winds falling through the day, no really strong
wind gusts are expected. And we could see a few more record high
temperatures today as well.

The weather will turn more active Sunday and especially Sunday
night and Monday as the next wave moves in from the south. We
did make a few tweaks this morning. For one, most guidance has a
slower arrival of the system. So we removed the POPs for late
tonight. And even on Sunday, the latest guidance is showing only
half of QPF for Sunday when compared to yesterday. The POPS we
have in the forecast might be the wettest it could be, and these
may need to be cut some more if trends continue. And with the
slower progression of the system, Sunday looks dry across
Central Wyoming. And it looks like one more mild day, with many
locations seeing high temperatures in the 60s once again. A
gusty wind will develop in the southwest flow locations from
Muddy Gap through Casper, but with 700 millibar winds only
around 35 knots, high wind is not expected.

The main part of the precipitation moves in Sunday night into Monday
as the upper level low lifts northward into Wyoming and we get the
best upper level divergence and jet dynamics. There continue
to be some differences in placement of the showers though. In the
deterministic model world, the European Model had around twice the
QPF of the GFS. It also spreads showers to most areas East of the
Divide while the GFS is largely dry, keeping most of the
precipitation to the western mountains. So, we turn to the world of
probabilistic forecasting, mainly the ensembles. Starting with
snowfall amounts, we first look at advisory level criteria, which is
6 inches in the mountains. The only locations showing at least a 1
in 2 chance of 6 inches or more are the higher elevations of the
Tetons, Wyoming Range and southwestern Yellowstone. The chance of 12
inches is basically zero. There could be some advisories issued, but
it is borderline right now. We still have time since impacts wouldn`t
begin until after sunset Sunday afternoon. With 700 millibar
temperatures remaining above 0 celsius through the day on Sunday,
and snow would be confined to the higher elevations. Cooler air
does wrap around Sunday night, with snow levels falling to around
6500 feet by Monday morning. The western valleys could see some
light accumulations but impacts at this time look negligible.
East of the Divide, snow levels should remain above 7000 feet,
keeping the populated areas likely almost all rain. QPF East of
the Divide also looks light, with at most a 1 in 4 chance of a
quarter inch or more except in the mountains.

This will be the transition into more typical November weather, as
the pattern looks more active as a trough moves into the western
United States. Flow is more westerly to even southwesterly for the
most part, so air will be Pacific, and this should keep temperatures
mainly only falling to near normal. A few systems will be moving
around Wyoming, but models are all over the place in regards to
timing and placement. So the reasoning remains the same as
yesterday. We have fairly high confidence of a cooler and more
active pattern, but the details of timing and amounts of
precipitation remain in flux.

&&



.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 354 PM MST Sat Nov 15 2025

Mid and high clouds continue to drift across the forecast area
overnight as all terminals remain VFR. An upper low along the
southern California coast tracks inland overnight and Sunday
morning, nearing Wyoming by midday Sunday. Southerly surface flow
ahead of this feature leads to an increase in southerly wind at KCPR
and KRKS around 18Z/Sunday. Isolated light showers approach from the
south Sunday afternoon with potential late day impacts across the
far west mountains and southwest Wyoming. Mid cloud heights do begin
to lower late in the day at terminals west of the Continental
Divide. Otherwise, winds remain light at all terminals through
the forecast, except KCPR and KRKS which will have gusts of 20
to 25 kt after 18Z.

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

&&

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

&&

$$

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...CNJ/LaVoie