253
FXUS65 KRIW 130430
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1030 PM MDT Wed Aug 12 2026

.KEY MESSAGES...

- Scattered showers and a couple isolated thunderstorms continue
  across northwest portions of the area, mainly Yellowstone
  through midnight. Some lightning and outflow winds up to 30 to
  40 mph possible.

- Showers and thunderstorms become more widespread on Thursday,
  with all locations seeing rain chances (60-80%).

- Cooler conditions with continued shower and thunderstorm
  chances persist into the weekend.

&&

.UPDATE...
Issued at 128 PM MDT Wed Aug 12 2026

Cooler and wetter conditions are (finally) ongoing across the area,
with this morning`s initial wave of showers now moving across
northern Wyoming. Additional shower and thunderstorm development is
expected shortly across southwestern Wyoming as instability builds
early this afternoon. This activity will spread northeastward
through the evening, with more isolated showers overnight. The
forecast for Thursday remains on track, with all locations seeing
decent chances for rain (60-90%). Cooler conditions with continued
rain chances persist into the weekend.

&&

.DISCUSSION...
Issued at 150 AM MDT Wed Aug 12 2026

A pattern shift is currently underway that will lead to chances for
precipitation each day through the rest of the week and through the
weekend. This shift will also put an end to the latest heat wave
with temperatures remaining at or slightly below normal through the
weekend. The culprits for this cooler and wetter pattern will be a
broad area of high pressure over the Deep South/Gulf Coast and a
longwave trough over the West Coast. The Cowboy State will be
sandwiched between these two features resulting in a moist
southwesterly flow pattern. Embedded shortwaves will rotate
northward over the region, bringing widespread chances for showers
and thunderstorms across the CWA each day through Sunday. The threat
for locally heavy rain will also return as monsoonal moisture will
return as well. Precipitable water values of 0.75" to 1" will be in
place across the region today and remain in place through the
forecast period. Chances for precipitation will increase over
western portions after sunrise this morning, spreading across areas
east of the Divide through the rest of the morning and continue
through the rest of the day. A separate wave of showers looks
to move over Sweetwater County after 20Z. Most showers will be
ending in the evening, with some lingering over the central
basins through 08Z Thursday. Any thunderstorm is likely to be
very isolated due to a lack of instability for the mostly
cloudy/overcast skies. These clouds will also be the reason why
temperatures will be 4 to 10 degrees cooler today. The
hazy/smoky conditions will begin to thin today, with improving
conditions expected by Thursday as the increased chances for
precipitation allow the atmosphere to become more mixed.
Additionally, the southwest flow aloft will cut off the source
region of most of the smoke (the large fire complexes in OR/WA).

Showers and possible thunderstorms will return across areas west of
the Divide by early Thursday afternoon and spread across the rest of
the CWA through the rest of the day into the evening. There will
still be a threat for locally heavy rain, with a higher focus over
Johnson County and portions of Natrona County. This will be due to
Gulf moisture advecting into the region, pushing PWAT values to
1.25" in this area. Strong thunderstorms are possible as well, with
forecasted CAPE values of 1500 to 2000 J/kg and a lifted index of
minus 4 to minus 6. However localized flash flooding will likely be
the highest threat as bulk shear will only be up to 30kt. WPC
Excessive Rain Outlook is also forecasting a Slight risk for
this area for Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1030 PM MDT Wed Aug 12 2026

VFR conditions throughout the period at all TAF sites. Lingering
light rain showers west of the Divide to include COD that will
slowly dissipate overnight ahead of another round Thursday
afternoon. All locations will see a decent chance for rain
shower activity (40-60%) with isolated storms near BPI/PNA
during the afternoon (20-30%). Any shower activity will linger
through sunset and push east/dissipate towards the end of the
period and overnight into Friday morning. Otherwise, relatively
light winds 10kts or less, except an occasional breeze at CPR
outside of the gusty outflow potential with storms near BPI/PNA.
There is a slight chance (10-20%) for MVFR ceilings at COD at
the end of the period and overnight Thursday but confidence low
but is mentioned as a 05Z line for this cycle.

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...

&&

$$

UPDATE...Myers
DISCUSSION...LaVoie
AVIATION...Lowe