156
FXUS65 KRIW 160431
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
Issued by National Weather Service Pueblo CO
1031 PM MDT Tue Jul 15 2025

.KEY MESSAGES...

- Lingering showers and storms this evening. Strong to severe
  thunderstorms will be capable of 60 mph winds, one inch
  diameter hail, and periods of heavy rainfall, until about 10
 PM.

- Rain chances end from west-to-east Wednesday afternoon and
  daytime highs Wednesday will be below normal.

- A warm-up begins Thursday and continues into the weekend with
  limited rain chances.

&&

.DISCUSSION...
Issued at 249 AM MDT Tue Jul 15 2025

Current (08Z) water vapor imagery shows an upper-level low
circulating near the British Columbia/Idaho border. At the surface,
a cold front extends from the upper low`s surface reflection and
across Montana. These features will help drive today`s active
weather.

The upper-level low will gradually shift into the region through the
day today. The surface cold front pushes south and situates itself
roughly along the Divide by mid-morning. On the west side of the
Divide, dry air and breezy westerly winds will create critical
fire weather conditions this afternoon across portions of
Sweetwater County where a Red Flag Warning has been issued.
Whereas behind the front northerly winds will usher moisture to
locations east of the Divide. Despite locations east of the
Divide being behind the front, temperatures will stay warm due
to 700mb temperatures between 10C- 12C and morning sunshine.

By early afternoon, a shortwave ahead of the approaching upper-level
low/trough combined with an associated 40-50kt supporting jet over
northwest Wyoming will provide sufficient support aloft for
widespread to numerous showers and thunderstorms, especially east of
the Divide. Mean SBCAPE values range from 1000-1500 J/kg, lifted
indices between -4C to -6C, and mean 0-6km shear between 30-50kts
all helps create an unstable atmosphere east of the Divide during
the afternoon and evening. These favorable upper-level dynamics and
unstable low-levels will support strong to severe thunderstorms
capable of at least 60 mph gusty winds and hail up to an inch. Thus,
a Slight Risk (level 2/5) has been introduced for an area
encompassing Fremont, Natrona, Johnson, Washakie, and Hot Springs
Counties. However all other locations east of the Divide remain in a
Marginal Risk (Level 1/5) for gusty winds around 60mph and isolated
severe hail. Additionally, mean PWATs east of the Divide range from
1.00" to 1.15" which is close to the daily maximum PWAT. These
abnormally high PWATs and deep warm cloud depths will favor heavy
rainfall; however, only isolated instances of flash flooding
potential exist given decent flow aloft to move thunderstorms.

West of the Divide is not out of the clear for convection this
afternoon either. Given the dry low-levels and inverted-V soundings
with dewpoint depressions between 40-60 degrees, mostly virga
showers and dry thunderstorms could create gusty 40-60 mph outflows,
especially across Sweetwater County.

The strong to severe threat diminishes through the evening as the
upper-level trough treks across the region late tonight. However,
there remains potential, mainly east of the Divide, for heavy rain
due to support aloft from increased PVA associated with the trough,
tall-skinny soundings, and abnormally high PWATs. Isolated to
scattered showers and thunderstorms exist again on Wednesday with
temperatures 20 to 25 degrees cooler than what we saw on Monday.

Ensemble model guidance is in consensus that zonal flow aloft will
be in place Thursday through the weekend. Warm and dry flow warms
temperatures back up into the 80s to 90s with limited chances for
showers and thunderstorms.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1030 PM MDT Tue Jul 15 2025

Showers will linger across central Wyoming tonight, with some impacts at KCPR
and KCOD. Low clouds will continue at KCOD and KCPR with IFR conditions through
Wednesday morning, improving to VFR Wednesday afternoon. Showers will end early
Wednesday morning with more scattered showers and storms near KRKS Wednesday
afternoon, with a PROB30 to cover this threat. Wind will be gusty at many
terminals Wednesday afternoon.

&&

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

&&

$$

UPDATE...CNJ
DISCUSSION...Gerhardt
AVIATION...NWS Riverton
FIRE WEATHER...CNJ/Gerhardt