Powder River, Wyoming Weather Forecast Discussion

003
FXUS65 KRIW 271942
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
142 PM MDT Sat Sep 27 2025
.KEY MESSAGES...
- Warm and dry weather returns today.
- Shower and thunderstorms will be possible over western
  portions Sunday and Tuesday.
&&
.UPDATE...
Issued at 128 PM MDT Sat Sep 27 2025
Not a whole lot to update in the short term. Nearly clear skies
continues through the rest of today with an above normal early
autumn day. Moisture still making progress northward across the
Four Corners region, which should be shifting across Wyoming
tonight. Models still have the cutoff low over southwest AZ
filling and sweeping northward on Sunday. With the weaker
outcome still favored, any shower activity on Sunday will be
more limited to the higher elevations of western WY where
chances of receiving rain accumulations over 0.10" remain low.
Monday rain chances also remain low, as the next longwave trough
along the west coast forces this weekend`s system quickly to
the northeast.
&&
.DISCUSSION...
Issued at 150 AM MDT Sat Sep 27 2025
Today will be the last quiet day for the next seven days, capping
out a mostly quiet week since last Tuesday. Clear skies, light winds
and seasonal to slightly above normal temperatures will be in place
today and tonight. A great day to enjoy the outdoors before fall and
winter really set in.
Clouds will begin to increase from the south this evening, spreading
northward through the overnight hours. These clouds will be from
moisture associated with a cutoff low that has been sitting over the
Desert Southwest for the last several days. Moisture will continue
to stream northward through the day Sunday, leading to isolated to
widely scattered (10-20%) showers and thunderstorms to occur over
mainly western portions of the CWA (along and west of a roughly Cody-
to-Rock Springs line) through the afternoon. Wind gusts of 40 to 50
mph will be the main threat, as T/Td spreads will be around 40
degrees. Any remaining shower or storm is expected to end by
midnight.
The cutoff low will begin to fill Sunday and get kicked from a
significant longwave trough over the EPAC. This trough will be the
focus for the next week. Precipitation will be even less across the
area Monday, as the remnant low moves northeast over CO and
southeast WY. The main effect from the low will be cooler midlevel
temperatures and continued southerly flow aloft. This will keep
temperatures near normal west of the Divide and slightly above
normal east of the Divide.
The longwave trough will move onshore over the West Coast Monday
night into Tuesday, filling and weakening as it does so. Showers and
thunderstorms will be possible over western portions Tuesday
afternoon as a result. The chances for widespread precipitation have
lowered quite significantly from yesterday, as model trends have the
trough much more shallower and staying more to the west and north.
Ridging will briefly build over the Cowboy State Wednesday, as the
upper low associated with the trough becomes better organized and
makes its way toward the Puget Sound area. This trend will continue
Thursday, but gusty southwest winds become more likely as the
gradient begins to tighten as the system begins to move onshore over
the PACNW. Elevated fire weather conditions look likely as a result
of this pattern. The timing of when this system moves over the CWA
remain in flux, as it could be as early as next Friday or it could
occur through the weekend.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1023 AM MDT Sat Sep 27 2025
VFR conditions will prevail through the TAF period. SKC skies to
start the period with mid to high level clouds gradually developing
during the late afternoon. Winds remain light generally under 10
knots with slightly greater winds around 10 knots at KCPR. A
nearing disturbance will bring increasing cloud cover overnight
into Sunday morning. Chances for showers begin to develop Sunday
morning and continue across western terminals through the end
of the TAF period. At this time confidence is not high enough
for any prevailing precipitation groups but that is subject to
change with the 00Z issuance.
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...Straub
DISCUSSION...LaVoie
AVIATION...Dziewaltowski

NWS RIW Office Area Forecast Discussion