147
FXUS65 KRIW 111714
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1014 AM MST Thu Dec 11 2025

.KEY MESSAGES...

- Gusty winds will gradually decrease today with afternoon high
  temperatures 20 to 30 degrees above normal.

- A cold front approaches northern Wyoming and bring mainly
  light snow, especially north of a Powell to Buffalo line.

- Most locations will see a continuation of above normal
  temperatures into next week with little to no precipitation
  chances.

&&

.DISCUSSION...
Issued at 210 AM MST Thu Dec 11 2025

If there is one thing that Wyoming is known for weather-wise,
it is the wind. The wind has been rather fierce around here for
the past couple of days, with a few gusts in the triple digits.
Thank you to a tight pressure gradient and the right front
quadrant of an 140 knot jet passing overhead. We still have a
few gusts over 75 mph, mainly around Chief Joseph Highway. But
the wind has backed off a few ticks in most areas early this
morning. But this is by Wyoming standards, this would be very
windy by most areas standards.

And that is the main forecast predicament we find ourselves this
morning. The High Wind Warnings will expire at 5 am this
morning. General trends are for the wind to continue decreasing,
as the jet is moving further north and the pressure gradient is
beginning to relax somewhat. The 700 millibar winds are finally
beginning to decrease, with all locations seeing them fall
under 50 knots by around noon today. Probabilistic guidance also
shows this trend, with chances of wind gusts over 50 mph
falling to less than 1 out of 4 for most populated areas by
noon. The exceptions are the usual suspects, mainly the south
side of Casper and near Cody. Some of the deterministic MOS
guidance does have a brief period of high wind around Casper
this morning before decreasing in the afternoon. There could be
a few stray high wind gusts at some of the mesonet sites, but
these tend to be on high rock bluffs away from populated areas
and have little impact. We will likely let the warnings expire,
but this will be a game time decision as we still hold the right
to extend them.

The second enigma (a problem, not the German new-age band
popular in the 90s), is what will happen tonight and tomorrow
across northern Wyoming. A cold front will sag southward toward
the area from Montana and likely bring some snow or rain turning
to snow across this location. I do get nervous when I see a
boundary with some jet energy here. Just about all guidance
keeps the best forcing over Montana and away from Wyoming. As
for snowfall amounts, Johnson County will be the most impacted
as far as the lower elevations. Chances of advisory amounts of
snow are low though. At Buffalo, there is only a 1 out of 6
chance of 3 inches or more with around a 1 out of 3 chance of 2
inches or more. As for the mountains, the most would likely fall
in the western Bighorn Range. A few locations have a 1 in 2
chance of 6 inches of more, but these are the highest
elevations away from the mountain passes. A small part of the
northern Absarokas has a 1 in 2 chance of 6 inches of snow or
more. However, this is also in a remote area and Beartooth
Highway is closed for the season. So, no advisory here as well.
The steadiest snow will fall from late tonight through Friday
morning before gradually ending Friday afternoon.

There is one more notable thing, high temperatures today. This will
especially be the case across central Wyoming. The MOS guidance has
high temperatures in the 60s in Riverton and in Casper. If it occurs
at the Riverton Airport, it would only be the fourth sixty
degree high in December in almost 30 years, and the latest by
nine days. In Casper, which has records back to 1939, it would
only be the fourteenth time in station history. Most locations
across the area will be 20 to as much as 30 degrees above normal
for high temperatures. It will cool off on Friday behind the
front, but most locations, except for where snow will be falling
will remain above normal.

Following that, it looks like we will enter into a quieter period.
Flat ridging will build across the area and bring mainly dry
conditions through Monday night. The next system looks to approach
the state on Tuesday or Wednesday from the west. With this
pattern, it would mean snow across the western mountains with
favorable upslope westerly flow with mainly dry conditions to
the east with downsloping. We could have another high wind event
though, as the pressure gradient looks rather tight and a
powerful jet, possibly over 150 knots, might be in place over
Wyoming. It is still a long way out, but the potential is here.
With the westerly flow, temperatures look to remain above
normal with no signs of arctic air masses for the next seven
days.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1014 AM MST Thu Dec 11 2025

The main weather impact through the period continues to be wind. A
cold front clips the northern part of Wyoming starting this evening,
with a northerly wind shift at KCOD/KCPR/KWRL around 03z. This front
brings increased clouds and precipitation chances, though any snow
chances are limited to northern Wyoming, and thus only at KCOD. The
northern flow could bring low (MVFR to IFR) ceilings at KCOD, KCPR,
and maybe KWRL through the end of the period. Confidence is not high
in how long these clouds would last, but current model indications
are ending them near the end of the period.

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...
High Wind Warning until 5 PM MST this afternoon for WYZ019-020-
022-030.

&&

$$

DISCUSSION...Hattings
AVIATION...Wittmann