301
FXUS65 KRIW 151105
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
405 AM MST Sat Nov 15 2025

.KEY MESSAGES...

- A dry and mild start to the weekend today with locally breezy
  conditions.

- A weather system will bring some rain and snow Sunday into
  Monday, with the greatest amounts in the western Mountains.

- A cooler and more active pattern still looks likely for much
  of next week, but details in regards to timing and amounts of
  precipitation remain uncertain.

&&

.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 /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 358 AM MST Sat Nov 15 2025

Mainly VFR flight conditions will dominate through 12Z Sunday.
The exception will be some local mountain obscurations across
the northern mountains until around 18Z Saturday. Gusty wind
will continue in vicinity of KCPR and KCOD through the day
today with gusts close to 30 knots in vicinity of KCPR and 25
knots near KCOD. Recent model trends have slowed the arrival of
precipitation on Sunday and any impacts on western TAF sites,
most notably KJAC, should hold off until after 12Z Sunday.
&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings