412
FXUS65 KRIW 100449
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1049 PM MDT Thu Oct 9 2025

.KEY MESSAGES...

- Chances for precipitation increase overnight across the
  southwest, spreading north through the morning and early
  afternoon on Friday with isolated showers continuing into the
  weekend.

- Another, more potent, disturbance will bring widespread
  chances for accumulating snow across western mountains for the
  second half of the weekend.

&&

.UPDATE...
Issued at 106 PM MDT Thu Oct 9 2025

There is not much change to the forecast. The HRRR continues to be
the more bullish model with regard to showers and thunderstorms
overnight through the day Friday. The focus of the precipitation
will generally be west of the Divide and snow levels will remain
high enough such that precip will be all rain. Brief heavy rain is
possible (10% chance), but the better moisture looks to be
Saturday/Sunday. HRRR and a few other Hi-res models do continue to
prog showers spreading east of the Divide Friday morning, with most
likely chances (20 to 30%) across the Wind River Basin and Bighorn
Basin. These could push into Natrona/Johnson Counties later in the
afternoon (20% chance), but models have been generally on a drying
trend with regard to afternoon shower activity. There does look to
be a pretty well defined dry air mass behind this wave of moisture,
that will keep much of the area dry through Friday night, though
isolated showers (mainly across the western mountains) do look to
remain possible (10 to 20% chances). The bigger push of tropical
moisture, coupled with the colder more potent trough still looks to
be on track for the Saturday night/Sunday time frame. Notably,
Saturday could also see the potential for severe weather and flash
flooding given the tropical moisture and instability with the
approaching trough/cold front. Chances are low (15%) at this time
for either threat, but worth noting.

&&

.DISCUSSION...
Issued at 221 AM MDT Thu Oct 9 2025

Warm and dry conditions persist across the Cowboy State today.
Temperatures this morning will still be on the chilly side,
especially across western WY. Temperatures this morning are expected
to range from the upper 20s to lower 30s west of the Divide and
upper 30s to lower 40s east of the Divide. Highs will be above
normal with temperatures in the lower to upper 70s across the
state. Near elevated fire weather conditions will be possible
once again this afternoon along the Wind Corridor from Rock
Springs to Casper. Winds will become breezy with periodic gusts
of 20 to 25 mph across the Wind Corridor. Min RH still remains
rather low sitting around 20%. Fire weather concerns will
quickly diminish by Friday as tropical moisture increases across
the area from the south and an unsettled active pattern
develops for the weekend.

There are a lot of moving parts regarding the upcoming forecast
for Friday through the weekend. The first thing to note is that
the time frame, as expected, has slowed down. The high pressure
that has been across the region through much of the week has
gradually shifted to the east. The center of the high will
settle over portions of Texas and New Mexico. The anticyclonic
flow should help funnel tropical moisture associated with
Hurricane Priscilla and its eventual remnants across parts of
the Desert Southwest starting today. This plume of monsoonal-
like moisture looks to eventually make its way into the southern
CWA by the early morning hours Friday. This may lead to a few
isolated showers and storms early Friday across Sweetwater,
southern Lincoln, and Sublette Counties and possibly further
north by the later morning hours Friday. Friday will have
chances for showers and storms, as above normal PWATs enter the
region. However, models have started to trend down on the
coverage of these showers with the best chances (20-50%) being
limited to southern and western WY. The bulk of the moisture
arrives by Saturday spreading further north across nearly all of
the CWA. Southwesterly flow enhances throughout Saturday aiding
with the funneling of moisture across much of the region. A
trough moving in from the PACNW will begin to shift east towards
the CWA. The nearing trough should provide some favorable
upper level dynamics that look to interact with the surplus of
tropical moisture. All of this should combine to create a push
of precipitation Saturday afternoon and evening across the CWA,
starting from the southwest into the central basins and
possibly northern areas. The nearing trough axis will supply
enhanced jet dynamics late Saturday into early Sunday over
western WY where flow looks to be the most favorable for a
period of upsloping. The trough will also bring with it colder
air leading to accumulating snowfall over the western
mountains. Lower elevations of western WY may see a brief
transition from cold rain to a wet heavy snow early Sunday
morning. Parts of the Jackson and Star Valleys may end up with
a wet slushy coating of snow by Sunday morning. Precipitation
will shift eastward through the day Sunday as the trough moves
across the state and to the east. Looking at snowfall amounts,
model guidance is showing a 30-60% chance for advisory criteria
amounts (6 inches or more) mainly across the higher elevations
of the Tetons, Absarokas and YNP, such as Pitchstone Plateau.

A brief lull in activity looks to occur Monday into Tuesday. Cold
temperatures may be possible as the trough moves out the area Sunday
night into Monday morning. There are early indications of widespread
sub freezing morning lows possible for Monday. Western WY may see
temperatures in the low 20s and possibly upper teens with lows
around the upper 20s east of the Divide. Still being a few days out
this may be subject to change. It is worth keeping an eye on
especially with some areas still not seeing a hard freeze yet.
Chilly temperatures will persist across the region with highs likely
in the 50s for Monday and Tuesday. The upcoming week is looking
messing and active with the potential for another disturbance moving
in from Canada for the middle of next week. Timing and impacts are
still very uncertain at this point and a better idea of what to
expect likely wont happen until the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1040 PM MDT Thu Oct 9 2025

High cirrus is starting to overspread the region as the next
weather system races in from the southwest. This will bring
increasing mid and high clouds through the night, with
increasing chances for showers around 12Z for sites west of the
Divide. Probabilities have improved with successive model runs,
so have added TEMPO groupings for these sites for higher
likelihood of rainfall, mainly between 12Z and 18Z. This area of
rain will have a lot of trouble getting east of the Divide, so
no rain notation here, except for a low possibility for KLND.
Once this wave moves through early afternoon, remainder of the
day remains mostly cloudy with ragged clouds at all levels. Next
round of precipitation is not expected before 06Z/11.

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

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

&&

$$

UPDATE...Hensley
DISCUSSION...Dziewaltowski
AVIATION...Straub