889
FXUS65 KRIW 161126
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
526 AM MDT Sat Aug 16 2025

.KEY MESSAGES...

- Overnight rain showers linger through Saturday morning.

- Another round of rain showers and isolated thunderstorms
  Saturday afternoon and evening with frequent lightning and
  gusty outflow winds the main hazards.

- Similar conditions Sunday with temperatures not as warm as it
  has been in recent days.

- Warming trend and dry conditions expected for much of next
  work week with the next chance for storm activity by week`s
  end.

&&

.DISCUSSION...
Issued at 130 AM MDT Sat Aug 16 2025

Current water vapor depicts southwest flow aloft across the CWA
with negative tilted ridging extending to the southeast into the
plains. IR shows a shortwave pushing out of northeastern Utah
that is giving way to some scattered rain showers into
Sweetwater County and even into far southern reaches of Fremont
County through the overnight into early Saturday morning.
Otherwise, these showers will diminish after sunrise with some
improving skies into the afternoon. With this, comes another
round of afternoon thunderstorms after 2-4PM west to east once
these showers and cloud cover dissipates south to north. That
will be the indicator on the evolution of these storms west of
the Divide and making it eastward through the evening. The
NAMNEST/HRRR have been doing fairly well on this the past couple
of days, and thus, carrying this over to Saturday. Storms west
of the Divide will be done by 00Z and then dissipate towards
sunset losing the limited instability after 03-04Z. The main
concern will be the frequent lightning for any more fire starts,
and then the gusty outflows for the ongoing fires. The big fire
in Hot Springs County will see these impacts between 02-03Z as
wind gusts are likely to push 40 mph with these storms and
possible more if they start to weaken and collapse off the
Absarokas prior to reaching east of Thermopolis. Cloud cover
could, and hopefully, diminish these impacts east of the Divide
and north of HWY 20 for these areas with the fires but something
to monitor as the afternoon progresses.

Otherwise, not as warm temperatures Saturday afternoon with the
aforementioned shortwave with temperatures in the 70s west of
the Divide and only in the low to mid 80s to the east. As such,
minimum relative humidity values will remain above the 20 to 30
percent range for these areas, but a bit lower south of the I-80
corridor a bit below 20 percent due to warmer temperatures with
more sunshine expected. Synoptic winds will be relatively light
less than 10 to 20 mph across the entire CWA outside of the
storm outflows, and as such, critical fire weather concerns are
not expected, although, elevated concerns still exist due to the
storm activity and its impacts.

Sunday and into much of next week, ridging extends in from a
high centered over the Colorado Rockies will inhibit any
monsoonal moisture from pumping in from the southwest. As such,
a warming trend and dry conditions expected for much of next
work week. Afternoon temperatures back into the 80s west of the
Divide and well into the 90s to the east. Wednesday afternoon
looks to be the hottest day in the extended forecast with
temperatures nearing the 100 degree mark. With that said, fire
weather conditions will increase with the warming trend as
relative humidity values will drop to critical thresholds but
will come to the winds as there are currently no indications of
stronger winds nor storm outflows of concern at this time. The
next chance for widespread storm activity will come Friday and
into next weekend as longer term models indicate a break down of
the upper level high with decreased convergence aloft pushing
east. This will allow the monsoonal moisture to pump back over
the CWA from the southwest with not as hot temperatures and
increasing precipitation chances to come.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 526 AM MDT Sat Aug 16 2025

Showers continue to move north at the start of the period. Gusty
south winds 25 to 30kt shave been fairly persistent across KLND and
KRIW along with KCPR for several hours. As the showers move through,
the winds should also diminish slightly, but wind gusts 20 to 25
will generally persist through much of the afternoon. There is a 30%
chance that the showers and gusty winds could make it to KWRL to
start the period as well. These showers will help to limit
convection, at least east of the Divide early in the afternoon.
Thus, expect to see showers and thunderstorms initiate west of the
Divide first, then spread east of the Divide later in the afternoon.
Timing of showers is covered with PROB30 groups for most terminals.
Shower and thunderstorms activity should decrease quickly after
02/03Z.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until 1 PM MDT this afternoon for WYZ003>006-
008.

&&

$$

DISCUSSION...Lowe
AVIATION...Hensley