Frost Lake Trail, Wyoming Weather Forecast Discussion

605
FXUS65 KRIW 202150
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
350 PM MDT Sat Sep 20 2025
.KEY MESSAGES...
- A few showers are expected through the afternoon, mainly limited
  to southern Wyoming.
- Shower and thunderstorm chances increase starting Sunday morning,
  with the best chances across western Wyoming through the day.
- A cold front will bring cooler and wetter conditions to all
  areas Sunday night through Monday night.
&&
.UPDATE...
Issued at 145 PM MDT Sat Sep 20 2025
The forecast remains on track today. There are a few light showers
across the southern half of the area in response to an upper
shortwave passing through. There will be a little more development
through the afternoon, though this will be pretty limited as a lobe
of drier air moves in from the west. As noted below, we do expect an
increase in coverage west of the Divide by sunrise Sunday as a
reinforcing shortwave and moisture arrives. This wave will be in
front of the main trough and approaching cold front and may lead to
some showers and thunderstorms moving east of the Divide as well
Sunday afternoon. This will be followed by the cold front sweeping
west to east beginning Sunday evening, bringing the main
precipitation event to the area through Monday night.
&&
.DISCUSSION...
Issued at 257 AM MDT Sat Sep 20 2025
We are now entering the last summer weekend of 2025, and it will be
a warm one to close it out. The basic reasoning of the forecast
remains the same as the previous couple of days. For most locations,
it will be a dry and warm start to the weekend, with
temperatures averaging 5 to 10 degrees above normal. There will
be a bit more convection around today though. Radar does show a
few showers in northern Utah and these are moving into southern
Lincoln County, but nothing appears to the reaching the ground
at this time. We made few changes to the placement today, with
showers mainly near the Unitas and up to around Afton, and even
here chances are low, only around 1 out of 4 at the most. Deeper
moisture and an approaching shortwave will keep showers and a
few storms going into the night, with coverage expanding to much
of the western mountains by sunrise Sunday. The bulk of the
showers should hold off until Sunday though.
And speaking of Sunday, a cold front will move into western Wyoming
and bring more widespread showers and thunderstorms for this time.
Most guidance has slowed a bit though in the eastern progression of
the front. As a result, most areas east of the Divide should be
largely dry through the daylight hours. And, with increasing
breezes as the pressure gradient tightens ahead of the front,
and better mixing, this could be the warmest day of the weekend
in places like Buffalo and Casper. There could be enough of a
breeze for elevated fire weather as well, although humidity and
wind does not look sufficient (only a 1 out of 5 chance) for
critical fire weather at this time. Although some showers are
possible Sunday evening east of the Divide, the bulk of the
precipitation should hold off until Monday.
We have some of the same concerns for early next week this
morning as we had yesterday. We have a high confidence (greater
than 9 out of 10) that it will be a much cooler day than Sunday
(possibly as much as 30 degrees cooler in northern Johnson
County). We have high confidence in a breezy day, with the
strongest wind in the favored cold advection / northwest post-
frontal locations like Johnson County where some 40 mph wind
gusts are likely. The continued uncertainty is with the
progression of the upper level low behind the front and
placement of the heaviest precipitation. There continues to be a
spread of around 18 hours as to when the low will move away to
the southeast, anywhere from later Monday night to Tuesday
afternoon, depending on what guidance you look at. And there is
little agreement on placement of the heaviest precipitation as
well. Generally, it looks to be in northern Wyoming but exact
locations are still up in the air. And finally, we still have
the likelihood of some snow in the higher elevations of the
northern mountains (generally above 9000 to 9500 feet). This
should not pose many travel concerns, but the highest locations
have at least a 1 in 2 chance of a couple of inches of new
snow.
Following the departure of the low, things look relatively tranquil
as ridging builds back into the area, bringing above normal
temperatures and mainly dry conditions through much of the middle
and end of next week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 350 PM MDT Sat Sep 20 2025
Winds generally lessen through this evening, though KRIW may be an
exception as northwest downvalley wind occurs. A shortwave
brings shower chances to southwestern sites between 15z and 18z.
These are mainly confined to KBPI, KJAC, and KPNA, though could
extend down to KRKS. With increased day time heating by mid-
morning, showers and thunderstorms will be possible through the
day Sunday, with PROB30 groups covering these chances. Best
chances remain along and west of the Divide, though a
shower/storm could move off the mountains, impacting KCOD or
KLND.
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...Hattings
AVIATION...Wittmann

NWS RIW Office Area Forecast Discussion