116
FXUS65 KRIW 241115
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
515 AM MDT Mon Aug 24 2026

.KEY MESSAGES...

- Another active weather day is in store today with most
  locations having a 30% to 50% chance of showers and
  thunderstorms. Showers or thunderstorms will be capable of 45
  to 60 mph winds, heavy rainfall, and frequent lightning.

- Shower and thunderstorms chances exist each afternoon Tuesday
  through the upcoming weekend. High temperatures each day this
  week are forecast to be in the 70s and 80s with lows in the
  40s and 50s.

&&

.DISCUSSION...
Issued at 241 AM MDT Mon Aug 24 2026

2:30 AM upper level water vapor imagery shows largely zonal flow
with an embedded shortwave disturbance over Wyoming, thanks to an
upper high centered over New Mexico. This disturbance has been the
focus for showers and a few thunderstorms across southern Wyoming
late Sunday night/early Monday morning. As this shortwave progresses
eastward through sunrise, coverage is expected to diminish with only
a few isolated showers across Sweetwater County. Temperatures today,
and most of this week, are forecast to have highs in the 70s and 80s
and lows in the 40s and 50s.

An active day is in store as another shortwave rounds the stagnant
upper high to our south. This shortwave looks to shift into western
Wyoming around noon/1PM Monday, allowing convection to take
advantage of peak heating (BL CAPE ranging from 500 to 1000 J/kg).
Most locations have a 20% to 50% chance of a shower or thunderstorm
this afternoon and evening due to abundant available moisture in the
mid levels of the atmosphere. Model forecast soundings are showing a
classic inverted-V profile and indicating DCAPE values around 1100
J/kg. Additionally, dew point depressions range from 45 to 55
degrees. These parameters suggest that thunderstorms will be capable
of 45 to 60 mph gusty outflows and this correlates well with the SPC
Day 1 Marginal Risk across much of Wyoming. Thunderstorms will also
be capable of frequent lightning and the potential for small hail
cannot be ruled out with steep mid level lapse rates. Showers and
thunderstorms are forecast roughly from Noon through at least 1AM
Tuesday, with the severe thunderstorm potential occurring between 1PM
and 9PM.

Given today`s shortwave will be working with monsoonal moisture and
PWATs around the 90th percentile of climatology, any shower or
thunderstorm will be capable of heavy rain and localized flooding.
It is important to note that storms will be moving today with cloud
layer shear in the 30 to 40kt range. The localized flooding issues
arise if multiple storms traverse over the same area. The current
forecasted QPF for today and tonight is a broad brushed 0.01 - 0.1
inches due to the overall scattered, but widespread coverage, nature
of storms today. It is very difficult, if not impossible, to pin
point the exact locations of showers and thunderstorms that could
traverse over the same area and/or produce heavier rainfall rates.

On Tuesday, the aforementioned upper high will build northwards into
the Great Basin with a ridge axis over Idaho. As this builds,
another shortwave, although weaker than today, is forecast to
traverse across Wyoming and bring additional shower and thunderstorm
chances. Flow will be more west to west-northwesterly with the
building ridge to our west, so monsoonal moisture is forecast to be
greatest across west, northwest, and northern Wyoming. Given the
weaker support aloft with overall height rises, showers and
thunderstorms on Tuesday afternoon are forecast to be largely
orographically and diurnally driven along and north of the
Continental Divide.

The upper ridge slowly shifts east across Wyoming on Wednesday and
Thursday with shortwave disturbances both afternoons. Wednesday
currently looks to have less coverage and be largely terrain driven
compared to Thursday. This is most likely due to height rises aloft
suppressing more numerous convective activity. As the forecast
currently stands, a more potent shortwave will be present as the
ridge shifts east out of Wyoming on Thursday. This means that
Thursday could be an active weather day for the area. Wyoming is
currently forecast to be in southwest flow behind the ridge Friday
through at least Sunday with embedded shortwaves each day. This
ultimately means that another weekend with afternoon showers and
thunderstorms is looking possible.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 513 AM MDT Mon Aug 24 2026

Showers and thunderstorms are forecast to develop across the state
after 18Z/19Z. All terminals have at least a 30 percent chance of
showers and thunderstorms at some point between the 19Z Monday and
06Z Tuesday. There is a reasonable amount of uncertainty with
regards to direct impacts and timing of convection, so maintained
PROB30s at this time. After the afternoon and early Monday evening
thunderstorm chances end, lingering rain showers are possible at
KJAC and KRKS and in the area of KCPR, KRIW, KLND, and KBPI. These
chances are reflected in additional PROB30 or VCSH groups. Any
showers or thunderstorms that are at or nearby a terminal will be
capable of 35 to 45 kt winds, frequent lightning, heavy rainfall,
and occasional mountain obscurations. Brief periods of MVFR to even
IFR flight conditions cannot be ruled out if a shower or
thunderstorm directly impacts a terminal. Otherwise, expect mid to
high level clouds throughout the TAF period. Outside of any showers
or thunderstorms, winds will generally remain around 12kts or less.
Occasional gusts around 20 kts are possible at KCPR and KRKS Monday
afternoon.

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...Gerhardt
AVIATION...Gerhardt