360
FXUS65 KRIW 021905
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
105 PM MDT Sat Aug 2 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms will move southwest to northeast
  across the area through the afternoon. Strong wind gusts of
  45 to 55 mph will be possible with this activity.

- Elevated to near critical fire weather conditions will continue
  across southern Wyoming through the weekend.

- Precipitation chances will be lower on Sunday, mainly limited to
  northern areas.

- Warmer and drier conditions are expected through much of next week,
  with temperatures returning to the upper 80s and mid 90s for
  most. Combined with gusty winds, this will lead to increased
  fire weather conditions during this period.

&&

.UPDATE...
Issued at 103 PM MDT Sat Aug 2 2025

Another round of showers and thunderstorms is kicking off early this
afternoon as a disturbance rotates through the ridge. Coverage will
be fairly widespread as convection moves from southwest to northeast
across the area. However, like yesterday, the drier surface layer
will keep much of the rain from reaching the ground. Accordingly,
strong outflow wind gusts of 45 to 55 mph will again be the primary
concern through the afternoon. This is backed up by the morning
sounding at KRIW and recent mesoanalysis data showing widespread
DCAPE values over 1000 J/kg. Showers and storms will taper off late
this evening, leaving decreasing clouds and lighter wind
overnight.

&&

.DISCUSSION...
Issued at 214 AM MDT Sat Aug 2 2025

The ridge that has been sitting across the central US, which has
given us a feed of monsoon moisture will be finally shifting
west the next couple days. Today will be the last widespread
moisture day, with scattered showers and thunderstorms
developing across the state during the early afternoon. Coverage
will be similar to the past couple days, with PW values still
near where they should be this time of year. Some thunderstorms
may again get strong, but these are getting more limited to the
open areas along and downwind of the Bighorn Range. Fire
weather concerns are somewhat elevated as humidity only
reaches 15 to 20% and some wind gusts near 20 in the afternoon,
but the very dry fuels across the state would still be very
responsive to any activity, including lightning.

Sunday will see the leading edge of drier desert air from the
desert southwest feeding into the state. This will start to
limit shower activity, with more shower activity not reaching
the ground, especially across SW WY. Best shower and
thunderstorm chances Sunday will be along and downwind of the
Absarokas and Bighorn Ranges during peak heating hours. Drier
air will also begin to increase the fire weather threat across
SW WY Sunday afternoon, as humidity levels west of the divide
tick downward to 10 to 15%, while more frequent wind gusts start
to show up.

By Monday the ridge will be settled on the Four Corners,
shutting down the moisture and increasing the heat. A passing
shortwave to the northwest may tap the last remnants of moisture
for showers along the Absarokas, but there won`t be much left to
precipitate by this time. This will bring temperatures upwards,
ranging form the upper 80s west of the divide, to the low to
mid 90s east. Humidity levels will be 8 to 14% each afternoon,
and wind gusts of 20 to 25 mph will be possible, so we may have
to contend with an extended period of elevated to critical fire
weather conditions.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1123 AM MDT Sat Aug 2 2025

The first in a series of shortwaves has been tracking across
southwest Wyoming Saturday morning. Another approaches from the west
later Saturday afternoon, with a final circulation set to trek
eastward across the forecast area tonight. Enough mid-level moisture
exists to generate scattered convection between mainly 20Z/Saturday
and 02Z/Sunday as the second shortwave crosses the region during
peak heating. PROB30 groups are the general rule and have tried
to narrow these to the most likely three- to four-hour periods
at each terminal Saturday afternoon. Moisture is mainly
confined above 500mb as noted on the KRIW and KSLC morning
soundings, therefore gusty outflow wind 30-40kts will be the
primary aviation hazard. The last shortwave is likely to keep a
few lingering light showers through the evening and perhaps into
the early morning hours Sunday across the far north and
southwest. Drier air arrives behind this final disturbance
leading to a quiet Sunday morning.

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...CNJ