Mammoth Hot Springs, Wyoming Weather Forecast Discussion

921
FXUS65 KRIW 081112
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
512 AM MDT Mon Sep 8 2025
.KEY MESSAGES...
- Isolated showers and thunderstorms will be possible again this
  afternoon, with southern portions of Sweetwater County having
  the better chances.
- Widespread elevated fire weather conditions are expected
  Monday through Thursday, with a focus on Wednesday and
  Thursday. Gusty southwest wind 20 to 35 mph is the primary
  hazard, mainly in southwest and central Wyoming.
- Afternoon and evening showers and thunderstorms are expected
  again Tuesday through Friday, with chances for widespread
  precipitation across the far west beginning Friday.
- Much cooler on Friday and Saturday as a weather system brings
  thick cloud cover and widespread precipitation chances to the
  area.
&&
.DISCUSSION...
Issued at 130 AM MDT Mon Sep 8 2025
Isolated showers will continue to end across the area early this
morning. A broad ridge will remain in place again today, allowing
for more drier air to move over the CWA. Any showers or
thunderstorms will be very isolated, with southern portions of
Sweetwater County having the better chances for any convection.
Additionally, elevated fire weather conditions will be in place with
RH values as low as 16 percent this afternoon. Winds will be
relatively light, with gusts of 15 to 20 mph. Locally higher gusts
up to 25 mph will occur across portions of Natrona County. The
smoky/hazy conditions should be improved this morning, with most of
the smoke having exited the region to the north/northeast. However,
additional smoke from wildfires in the Sierra Nevadas will move over
western portions through the afternoon.
An upper level low will move onshore over OR later this afternoon
and dig southward over northern CA tonight through Tuesday. This
will cause the ridge axis over the Cowboy State to amplify and
gradually shift eastward through the day Tuesday. This eastward
shift will allow the winds aloft to turn more southwesterly. Subtle
shortwaves and Pacific moisture will move over the CWA through the
afternoon as a result. PWATs will increase, but will not be as high
as they have been the last few days. Values will range between 0.5
to 0.7" Weak showers will be possible over far southwestern portions
by 08Z Tuesday and gradually dissipate as they to move to the
northeast through 13Z. Showers and thunderstorms will be widely
scattered (20-30% chance) across the forecast area through the
afternoon, as additional shortwaves move over the area. Wind gusts
of 35 to 45 mph will be the main threat. Any smoke will once again
get pushed northward out of the area through the day.
This overall pattern will continue Wednesday and Thursday, as the
upper level low slowly rotates over portions of OR, CA, NV and ID.
The southwest flow aloft will continue over the Cowboy State, as a
high develops over west TX and strengthens the ridge over the
Plains. These winds will usher in more drier air once again and set
up a pseudo-dryline along the I-25 Corridor Wednesday afternoon. Any
convection looks to be confined to western portions of the state and
by isolated through the afternoon and overnight hours. Wednesday
also looks to be the strongest day for possible critical fire
weather behavior. Although RH values are expected to stay above
critical thresholds (15%), 700mb winds up to 30 kt will be
widespread across much of the CWA. Thursday doesn`t look to be as
critical, as RH values will be slightly higher and 700mb winds will
be lower, around 20 kt. Any convection looks to remain very isolated
Thursday, with most of the activity being focused over southeastern
portions of the state.
Isolated showers will be possible over western portions Thursday
night into Friday morning, as the eastern fringes of the upper low
approach. Temperatures will be 10 to 15 degrees cooler Friday, as a
result of this low. Cloud cover will certainly aid in these cooler
temperatures. Precipitation chances will quickly increase over
western portions Friday afternoon, as a portion of the low rounds
the base of the trough and moves northward. Precipitation will
become widespread across the forecast area through the overnight
hours, as the low moves over southwestern portions by 12Z Saturday.
Precipitation chances will be varied Saturday and be highly
dependent on the track of the low. Regardless, temperatures will
remain on the cool side with highs in the 60s west of the Divide and
lower to middle 70s east of the Divide. Freezing temperatures could
occur for portions west of the Divide Friday and Saturday nights in
the more cold prone locations, like Cokeville and Bondurant.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 511 AM MDT Mon Sep 8 2025
A very isolated shower or two may linger nearby some terminals east
of the Divide to start the TAF period, regardless VFR
conditions are expected to prevail. Clouds will gradually clear
through the morning before returning for the afternoon and
evening. Winds remain light through much of the period with a
slight increase at nearly all terminal during the afternoon.
Brief gusts around 15 to 20 knots will be possible this
afternoon, winds decrease and become light by the evening.
Isolated showers and possibly a thunderstorm may develop this
afternoon into the late evening with most terminals seeing
little to no impacts. The main concern would be brief gusty
outflow winds around 30 knots nearby any showers or storms. Some
mountain obscuration may be possible as showers develop this
afternoon and evening.
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.
&&
$$
DISCUSSION...LaVoie
AVIATION...Dziewaltowski

NWS RIW Office Area Forecast Discussion