Moose, Wyoming Weather Forecast Discussion

259
FXUS65 KRIW 131912
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
112 PM MDT Sat Sep 13 2025
.KEY MESSAGES...
- Isolated showers and thunderstorms are expected through this evening.
  Outflow wind gusts to 30 mph are the primary concern.
- After a warmer and drier end to the weekend, unsettled
  conditions will return through early next week bringing
  additional shower and thunderstorm chances.
- Morning lows will continue to trend seasonably downward. Temperatures
  across basins west of the Divide may approach or drop below
  freezing early next week.
&&
.UPDATE...
Issued at 109 PM MDT Sat Sep 13 2025
The forecast is on track early this afternoon with two distinct
areas of interest evident on water vapor, both associated with the
broad trough stretched across the area. One is across northwestern
Wyoming where visible imagery and radar continue to show an area of
showers slowly rotating east. The other is across southern Wyoming
as moisture moves north out of Colorado. With this additional
moisture and continued diurnal destabilization we are beginning to
see more shower and thunderstorm development; this will continue
through the afternoon though coverage will be fairly isolated.
The best chance for additional accumulation will be across the
western and northern mountains. This activity will end late this
evening with clouds clearing from west to east through the
overnight hours. Brief ridging will make for a drier and warmer
Sunday.
&&
.DISCUSSION...
Issued at 203 AM MDT Sat Sep 13 2025
The broad midlevel trough continues to move eastward across the
Rockies this morning, as evidenced well on the latest WV
imagery. The initial lobe wrapping around this trough is noted
spinning across NW WY currently, with multiple meso spins noted
on radar. This continues to enhance shower activity this
morning, which will continue to produce welcome rainfall. As
this initial lobe sweeps to the northeast, wraparound energy
will still be able to produce showers and thunderstorms for the
NW corner of the state this afternoon once daytime heating picks
up. Ample moisture is in place, with last night`s PW value at
0.72", which is in the 90th percentile for this time of year. So
any rainfall that does fall should efficiently produce
rainfall. Current forecast for accumulations could reach near a
half inch across the northern Absarokas through sunset tonight.
Models note the next piece of the trough sweeps across Colorado
into western Nebraska/South Dakota tonight into Sunday. This
will focus the next round of rainfall mainly farther east
across eastern WY. The western edge of this precip will approach
eastern Sweetwater County and the eastern fringes of Natrona
County during this period. Where the trough finally moves will
determine if any rainfall falls in these locations. In between
these two parts of the trough, generally from western Sweetwater
County to Fremont County to most of Johnson County will remain
mostly dry today and tomorrow, with mild temperatures in the
70s. A couple showers are not out of the question in these
areas, but any accumulations would remain low.
The next piece of the trough rotates through from the west
Sunday night into Monday, bringing the next round of rainfall.
While most of the remaining moisture has already been drawn into
the central Plains by this time, there will still be enough
moisture and lift to spark showers during the day Monday,
sweeping eastward. The overarching longwave trough will be
settled across the region by this time, which will keep the
threat for showers continuing further into midweek. Models
start to differ after this time, mainly differing on the speed
that the trough finally moves east, so any precip forecast
beyond Wednesday remains lower confidence at this juncture.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1108 AM MDT Sat Sep 13 2025
Scattered showers and thunderstorms will be around through this
evening. All locations have a chance to see a shower/storm. Highest
chances will be over northwest Wyoming, nearest KCOD and KJAC. Main
hazard with storms are outflow gusts around 30 knots. Most lingering
showers should end by around midnight. A clearing sky tonight, in
combination with the cooler temperatures and (potential) recent
rainfall, could bring some fog development. Confidence is too low as
of now to include in TAFs.
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...
None.
&&
$$
UPDATE...Myers
DISCUSSION...Straub
AVIATION...Wittmann

NWS RIW Office Area Forecast Discussion