770
FXUS65 KRIW 110916
AFDRIW

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

.KEY MESSAGES...

- Wind will gradually decrease today with a continuation of well
  above normal temperatures.

- A cold front will approach 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.

&&

.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 to triple digits. Thank you to a
tight pressure gradient and the area in the right front quadrant of
an 140 knot jet. 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 sights,
but these tend to 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
though 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 /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 945 PM MST Wed Dec 10 2025

VFR conditions at all TAF sites to start the period and much of
Thursday. Windy conditions persist at COD/CPR/RIW overnight with
a persistent westerly flow aided by a low level jet pushing
over Yellowstone. Mid and upper level clouds throughout the
period increasing in coverage late after 00Z with the next
system. With that, winds stay elevated at all TAF sites, highest
at RKS up to 30kts and other locations 18-25kts. With the
aforementioned system skirting to the north, only COD will see
a chance for snow on station after 03Z and into the next TAF
cycle. Indications are for at best MVFR conditions with possible
IFR after this point in time. Mid level ceilings at all other
sites linger overnight into Friday before lifting and all
remaining dry into the weekend.

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 AM MST early this morning for WYZ019-
020-022-028>030.

&&

$$

DISCUSSION...Hattings
AVIATION...Lowe