258
FXUS65 KRIW 010440
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
940 PM MST Sun Nov 30 2025

.KEY MESSAGES...

- Remaining cloud cover dissipates or moves south and east of
  the region by early Monday morning leaving a clear sky and
  below normal overnight lows.

- Monday is dry and high temperatures warm a few degrees. Breezy
  afternoon westerly wind 20 to 30 mph occurs over southwest
  Wyoming and into Natrona County.

- The next wintry weather system arrives in western Wyoming
  Monday night and Tuesday. Light snow gradually spreads east of
  the Continental Divide Tuesday evening and persists through
  the Wednesday morning commute.

- Northwest flow aloft favors additional light snow in the
  western and northern mountains late in the week. Temperatures
  across the region remain seasonal heading into next weekend.

&&

.UPDATE...
Issued at 1119 AM MST Sun Nov 30 2025

No major changes with today`s forecast. A quick-moving weather
system brings light snow to southern Wyoming through this evening.
It seems to be slightly further south than previous models had,
resulting in snow amounts coming down ever so slightly, with chances
decreasing across Jackson Valley and the northern Green River Basin.
The main impacts remain to be for any travel along I-80 and southern
Lincoln County, were some snow and breezy winds (20 to 25 mph) could
cause minor winter travel conditions through about sunset.

&&

.DISCUSSION...
Issued at 201 AM MST Sun Nov 30 2025

It is a quiet, but rather cold night here at the humble
Riverton weather abode. Some locations are having their coldest
temperatures so far this season. Things will turn a bit more
active again today though.

The culprit for this is a weak area of low pressure that will drop
across Idaho and then into Utah and Colorado today. This does
not look like a big storm for us given that the system is fairly
moisture starved and the best dynamics will remain to the south
of Wyoming. As a result, snowfall amounts look relatively
small. Ensemble guidance gives at most a 1 in 3 chance of 2
inches or more in the southern Star Valley and southern Lincoln
County, with most other lower elevation locations having at
most a 1 in 2 chance of an inch of snow. Nevertheless, there
could be some impacts on a busy travel day at the end of the
Thanksgiving holiday weekend, including Interstate 80. Not
enough for an advisory though. The highest amounts will occur in
the Salt and Wyoming Ranges, but even here there is only at
most a 1 in 3 chance of 4 inches across the higher peaks with a
near zero chance of 6 inches. As for elsewhere, a few snow
showers could jump the Divide but any amounts east of the
Divide would likely be slim to none. The time of most impacts
would be from around 9 am to 4 pm, with all snow ending by
midnight tonight as the system moves away to the south and east.
Otherwise, expect another cold day with temperatures averaging
5 to 10 degrees below normal under mostly cloudy/overcast skies.

High pressure should bring a dry start to the work week on Monday
with temperatures climbing closer to seasonal normals, as our
air mass modifies a bit. There will be a gusty wind in the
Wind Corridor from Rock Springs through Casper ahead of the
next weather system. This system will bring impacts for Tuesday
into Tuesday night. Most areas have the potential for more
accumulating snow. Ensemble guidance gives much of northern and
central Wyoming at least a 1 out of 3 chance of 2 inches of snow
or more, although again this does not look like a major storm,
with the chance of 6 inches or more generally less than 1 out of
4 except in the mountains. The problem with this system is that
there are a lot of moving parts and guidance still has a rather
substantial spread on most aspects including timing and
placement of the heavier snow. So, confidence is fairly high
there will be some snow, but exact details are still uncertain.
Then, after a dry Thursday, another system may approach for the
end of the week and next weekend. Like Tuesday`s system, there
is still a decent spread in guidance and details are difficult
to resolve this far out. Temperatures should average fairly
close to seasonal normals, with the coldest temperatures
expected Wednesday behind the next cold front. However, no
arctic outbreaks are expected for the next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 940 PM MST Sun Nov 30 2025

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Terminals

All terminals to remain VFR through at least 00Z/Tuesday. North to
northwest flow aloft prevails through much of Monday before backing
slowly to the west ahead of an approaching weather system late in
the period. This system/shortwave and associated Pacific moisture
reaches far west Wyoming after 00Z/Tuesday. In general, this leads
to little more than lowering mid and high cloud decks. However,
low-end VFR conditions and the potential for nearby snow showers
arrive at KJAC after 03Z/Tuesday. As for surface wind, expect KRKS,
KBPI, and KPNA to see increasing west to northwest wind between
17Z-21Z/Monday. KRKS will be earliest and strongest Monday at
14-28kts. Wind speeds at these terminals decrease around
00Z/Tuesday, although not as much at KRKS. Mountain tops
occasionally obscured after 02Z/Tuesday.

East of the Continental Divide...KCPR/KCOD/KRIW/KLND/KWRL Terminals

All terminals to be VFR through the forecast period in north to
northwest flow aloft in advance of an approaching shortwave. Little
more than increasing high clouds Monday, with a developing mid-cloud
deck after 00Z/Tuesday as Pacific moisture spills east of the
Divide. Gusty southwest surface wind increases to 12-25kts at KCPR
late Monday morning and diminishes around 00Z/Tuesday. KCOD could
see westerly wind develop Monday afternoon, but the better chance
comes shortly after sunset. Similarly, KRIW could see gustier
west-northwest wind after sunset as well, but this may hold off
until after 06Z/Tuesday if it occurs at all.

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

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...CNJ