496
FXUS65 KRIW 301113
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
513 AM MDT Mon Jun 30 2025

.KEY MESSAGES...

- Mostly dry and warm today and Tuesday with shower and
  thunderstorm coverage increasing Wednesday, continuing through
  the end of the week. Locally heavy rain possible with the
  storms Wednesday, increasing to localized flash flooding
  Thursday.

- Hottest days this week are Tuesday and Wednesday, with
  widespread highs in the 90s.

&&

.DISCUSSION...
Issued at 123 AM MDT Mon Jun 30 2025

The cold front that dropped southward Sunday morning will continue
its progression across the CWA this morning, bringing easterly winds
across southern portions. The front will eventually stall and wash
out by midday as winds west of the Divide turn more southwesterly.
Dry conditions will result across most of the area today, as an
upper level ridge builds over the Four Corners to the northern end
of the Great Basin. Temperatures will remain seasonal with light
winds and mostly clear skies. Some high-based CU will build over the
western mountains late in the afternoon. Today will be the quietest
day of the week.

The aforementioned ridge, in combination with a closed low just off
the CA coast, will allow for an increase in moisture from the south
beginning on Tuesday and continue into Wednesday. This could be the
start of the monsoon season. Hot temperatures return Tuesday, with
readings in the upper 80s to near 90 degrees west of the Divide and
readings in the 90s east of the Divide. Virga showers/thunderstorms
are likely (as CAPE values will be up to 500 J/kg) with a 20-30%
chance to occur over western and central portions of the CWA. This
activity looks to develop after 20Z and gradually end across much of
the area through sunset. The main threat will be wind gusts of 50 to
60 mph, as dewpoint depressions will be quite large (45 to 60
degrees difference). Isolated showers may linger through the
overnight hours, but details are fuzzy at this time.

Convective activity looks to remain somewhat limited and more
isolated Wednesday, as CAPE values will be around 500-800 J/kg and
lifted indices of minus 2 to minus 4. This in despite of increasing
moisture and precipitable water values increasing to 0.6" to 0.9".
This will introduce the potential for heavy rain as an additional
threat for thunderstorms.

The closed low will begin to weaken and fill as it moves onshore
Wednesday night and the ridge shifting eastward over the Plains,
resulting in a more southwesterly flow aloft. This will also result
in PWAT values approaching (and possibly exceeding) 1 inch. This
will be near record levels as the max value for early July is around
0.96". The remnant low will move over the Four Corners during this
time, heading toward southwestern portions of the Cowboy State. The
added lift from this low (and additional subtle shortwaves ahead of
the low) will add to the lift for widespread showers and
thunderstorms. The increasing PWAT will also add to this buoyancy.
Most of the convective activity looks to be over mainly western
portions Thursday afternoon, spreading eastward across the rest of
the forecast area through the evening. Needless to say, localized
flash flooding could occur with the stronger storms in the afternoon
and early evening.

The flow pattern becomes a bit flat for the Fourth of July (Friday),
as the remnants of the low continue to slowly propagate eastward.
This would result in the thunderstorms being more focused over areas
east of the Divide. Another round of thunderstorms is possible
across western portions Saturday afternoon, as a shortwave moves
over southern ID.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 513 AM MDT Mon Jun 30 2025

VFR conditions across all terminals throughout the TAF period. Skies
will be SKC for the most part with a few patches of high cirrus
possible during the afternoon and evening. Winds remain mostly light
with a brief period of breezy winds possible at KCPR and KWRL during
the evening Monday. Most terminals east of the Divide will see a
slight shift in wind direction from easterly during the day to a
westerly component by the end of the TAF period.

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...LaVoie
AVIATION...Dziewaltowski