874
FXUS65 KRIW 071129
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
529 AM MDT Sat Jun 7 2025

.KEY MESSAGES...

- Widespread warm temperatures with mostly sunny skies today
  with shower and thunderstorm chances (30-70%) across the
  Bighorn Basin, the Bighorn Mountains, and Johnson County late
  this afternoon and evening.

- Near elevated fire weather conditions are possible this
  afternoon across southern Wyoming with low relative humidity
  values between 15-20% and gusty winds up to 30 mph.

- Much above normal temperatures are forecast the first half of
  the work week with multiple shower and thunderstorm chances
  Tuesday onward.

&&

.DISCUSSION...
Issued at 223 AM MDT Sat Jun 7 2025

As of 2AM local, water vapor imagery shows a weak shortwave
traversing the Intermountain West and bringing increased cloud
cover. The shortwave is expected to be east of the CWA shortly after
sunrise this morning, leaving mostly sunny skies much of the
day today. Wyoming will largely be situated between a building
upper-level ridge to the west and an upper-level trough the
northeast, leaving the region in northwesterly flow aloft today.
With mostly sunny skies, gusty winds between 20-30 mph, and
700-mb temperatures between 8-12C, temperatures will be allowed
to warm to slightly above normal today (70s to low 80s F). Gusty
winds and low relative humidity values between 15-20%,
especially across the southern portion of the state, supports
near elevated fire danger this afternoon.

In addition to the warm temperatures, an area of increased PVA is
forecast to round the trough and traverse the northern portions of
the state, providing support for isolated to scattered thunderstorm
chances primarily across the Bighorn Basin, the Bighorn
Mountains, and Johnson County. Convection chances (30-70%) will
increase during the late afternoon/evening. CAPE values are
forecast around 500 J/kg during this timeframe. However,
thunderstorms are not forecast to become severe with overall
height rises and modest mid-level lapse rates. The strongest
storms could produce gusty outflows up to 40mph. Storm coverage
diminishes after sunset with only isolated to scattered showers
possible (up to 50% chance) during the overnight hours across
Johnson County and the southern half of the Bighorn Mountains.

A somewhat similar pattern is in store on Sunday with the main
difference being that the upper-level trough is pushed farther
east as the ridge slowly shifts into the region. This ultimately
helps keep the area largely shower and thunderstorm free apart
from high elevation showers. High temperatures on Sunday are
forecast to be slightly cooler than today for locations east of
the Divide with 700-mb temperatures forecast to be less than
8C.

Ensemble guidance remains in consensus that the upper-level
ridge will be overhead Monday through Wednesday morning. Height
rises aloft and 700-mb temperatures around 12C will favor a warm
up to temperatures nearly 10-15 degrees above normal on
Tuesday. By Tuesday evening, there is consensus in a weak
disturbance rounding the ridge and bringing the next chance of
precipitation to portions of the area. However, there remains
uncertainty with the Tuesday system with the amount of
available moisture which will ultimately effect precipitation
chances. The ridge axis is forecast to be well east of the
Intermountain West by midday Wednesday leaving the region in
west-southwest flow through early next weekend. Deterministic
guidance is hinting at a frontal passage on Wednesday brining
more widespread precipitation, however, given how far out this
is, details remain unclear.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 526 AM MDT Sat Jun 7 2025

Northwest flow aloft will settle over the area for the next 24 hours
as a ridge slowly develops across the western US. Skies will be
mostly clear for most terminals through Saturday afternoon,
with some mid- level (FL100-150) clouds moving in Saturday
evening. Wind will increase for much of the area Saturday
afternoon, with sustained wind of 10-15 knots and gusts of 20-25
knots at most terminals. As the weather system slides through
from the north Saturday evening a northerly wind shift will
accompany it, which will be most noticeable at terminals east of
the Continental Divide. This shortwave will also bring the
increasing cloud cover, and an isolated rain shower or
thunderstorm is possible (10-15%) at KCOD and KWRL Saturday
evening as a weak weather system slides down from the north, but
confidence is not high enough to include in the TAF. KCPR will
also see shower chances increasing late in the period (towards
12Z Sunday), but again, not enough confidence to include
mentions in the TAF.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

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

&&

$$

DISCUSSION...Gerhardt
AVIATION...Hensley/Rowe