292
FXUS65 KRIW 250432
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1032 PM MDT Mon Aug 24 2026

.KEY MESSAGES...

- Scattered thunderstorms continue through the evening hours for
  the southern half of the viewing areas. Gusty outflow winds
  and frequent lightning the main hazards through sunset.

- Thunderstorm activity diminishes through the overnight with
  Tuesday morning low temperatures 2 to 5 degrees cooler than
  Monday leading to similar setup for the rest of the day.

- Shower and thunderstorms chances exist each afternoon 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.

&&

.UPDATE...
Issued at 1231 PM MDT Mon Aug 24 2026

With this update, have refreshed precipitation chances with the
latest hi-res models. Overall, no major changes were made, with
fairly widespread 20 to 60 percent chances. Chances drop below 10
percent across far northern Wyoming, except for around Yellowstone
between 7pm and midnight when some rain chances may move through.
Otherwise, the focus for today remains on the storms, which continue
to show potential for gusty outflow winds. The latest HRRR depicts
some gusts up to 60 mph, especially across western and southern
Wyoming.

&&

.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 /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1030 PM MDT Mon Aug 24 2026

VFR conditions currently and through the entirety of the period.
Ongoing showers and some isolated thunderstorms pushing east of
LND/RIW and nearing COD for the first hour or two of the period
into the overnight hours. Otherwise, mid level clouds into
Tuesday morning with light winds. Winds remain relatively light
around 10kts or less outside of a brief gust at RKS after 20Z
with daytime heating up to 18kts. Thunderstorms develop once
again with HiRes data still not in line with each other similar
to Monday but consensus is not as active, however. PROB30 groups
after 20Z for BPI/PNA, 21Z for COD/RIW/LND, and 22Z for WRL
through 00-02Z respectively. Lower but VFR ceilings and gusty
outflows up to 35-40kts possible with the strongest cells
through the mid afternoon to early evening hours. Storms exit to
the east there after and weaken, with mid level clouds and
light winds once again to end the period heading into Tuesday`s
overnight hours.

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.

&&

$$

UPDATE...Wittmann
DISCUSSION...Gerhardt
AVIATION...Lowe