234
FXUS65 KRIW 161204
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
Issued by National Weather Service Billings MT
604 AM MDT Wed Jul 16 2025

.KEY MESSAGES...

- Isolated to scattered, mostly virga showers/dry thunderstorms
  are expected across southern Wyoming this afternoon. These
  virga showers/dry thunderstorms will be capable of around 40
  mph outflows.

- Below normal temperatures east of the Divide and near normal
  temperatures west of the Divide today. Elevated fire weather
  conditions exist today across southern Wyoming, especially the
  Green River Basin.

- Warmer temperatures return on Thursday through at least early
  next week. The greatest shower and thunderstorm chances exist
  Friday and Saturday afternoons.

&&

.DISCUSSION...
Issued at 309 AM MDT Wed Jul 16 2025

The upper-level trough that drove Tuesdays thunderstorms will
be over the Upper Great Plains by early afternoon, leaving
Wyoming in zonal flow aloft. At the surface, a frontal boundary
will remain stationary along the Divide. East of the Divide,
saturated northerly flow will keep temperatures much cooler than
what we have been experiencing the past week or so.
Temperatures here will be about 5 to 12 degrees cooler today (in
the 60s and 70s), which will be 10-20 degrees below normal for
mid-July.

West of the Divide, unsaturated westerly flow with mean 700-mb
temperatures will keep temperatures largely near normal today.
Deep mixing in conjunction with the already unsaturated westerly
flow, will help drop relative humidity values to around 15-20%
west of the Divide with the lowest values across the Green River
Basin. The surface pressure gradient will remain somewhat tight
west of the Divide, leading to west-northwest winds gusting 20
to 30 mph. Critical fire weather conditions will be marginal and
not widespread, as a result at this time, thus no highlights
are being issued. However, with the westerly winds being
funneled down the Green River Basin, relative humidity values
below 15% is not completely out of the question this afternoon.

An embedded disturbance aloft is forecast to trek across
southern Wyoming late this afternoon and evening and provide
support for isolated to scattered showers and thunderstorms
across Sweetwater County. With mean SBCAPE forecasted around 500
J/kg at its highest and 0-6km shear around 20kts, storms are
not expected to become severe. However, given the dry low-levels
with dewpoint depressions between 30-40 degrees a virga shower
or dry thunderstorm will be capable of producing gusty outflows
around 40 mph.

Ensemble model guidance is in consensus in zonal flow aloft and
weak unsaturated low-level flow on Thursday. This will begin
the first day of a warm up to near to above normal temperatures
across the entire area. By Friday afternoon, an upper-level low
develops over southern California and a trough begins developing
over the Pacific Northwest and this set-up ushers in increased
moisture into the Intermountain West. This increased moisture
aloft and a weak disturbance aloft will support afternoon
isolated to scattered showers and thunderstorms across southern
Wyoming and east of the Divide Friday afternoon. These scattered
shower and thunderstorm chances are expected again on Saturday
across southern Wyoming as another disturbance treks across the
area and a surface boundary situates itself near the southern
Wyoming border. Drier weather and near normal temperatures are
expected to return Sunday through early next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 455 AM MDT Wed Jul 16 2025

Showers and isolated thunderstorms are ongoing over northern
portions of the CWA this morning. These showers have pushed east past
KCOD and KWRL terminals, but will likely impact KBYG from 12Z to 15Z.
VLIFR to LIFR conditions are in place at KJAC and KCOD, with conditions
expected to improve at KJAC after sunrise and VFR conditions returning
by 16Z. LIFR to MVFR ceilings will remain in place across northern
portions throuygh 18Z/19Z. MVFR ceilings are expected to develop over
the Wind River Basin after sunrise, with VFR conditions returning by 17Z/18Z.
Showers and thunderstorms will redevelop over southern portions this
afternoon, impacting KRKS between 21Z and 01Z. Wind gusts around 25 kt
will also impact terminals west of the Divide, except KJAC. Clouds
will scatter out across the west this afternoon, with SKC skies in place
for most areas by sunset this evening. Lingering SCT-BKN FL040 clouds over
portions of Johnson/Natron counties through the TAF period.

&&

.FIRE WEATHER

Issued at 602 AM MDT Wed Jul 16 2025

Elevated to near critical fire weather conditions are expected
across southern Wyoming today. Minimum relative humidity is forecast
be around 15-20% with westerly gusts between 20-30 mph, especially
across far southwest Wyoming (277) and the Green River Basin (zone 278).
Given uncertainty in relative humidity values falling below 15% across
the aforementioned zones, no highlights have been issued at this time
(5AM local). That being said, deep mixing with gusty winds could drop
relative humidity values more than what is currently forecast.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Gerhardt
AVIATION...LaVoie
FIRE WEATHER...Gerhardt