222
FXUS65 KRIW 140806
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
206 AM MDT Sat Jun 14 2025

.KEY MESSAGES...

- Thunderstorms occur this afternoon and evening, mainly for
  locations along and east of the Continental Divide. Strong to
  severe storms are possible around Johnson County and the
  Bighorn Mountains between 3pm and 11pm MDT. Large hail and
  strong winds are the main hazards.

- Elevated fire weather conditions occur across southern
  portions of the area today through Monday.

- Daily thunderstorm chances continue through Tuesday, mainly
  for areas along and east of the Divide. Some storms could be
  strong to severe.

&&

.DISCUSSION...
Issued at 205 AM MDT Sat Jun 14 2025

Today features a similar story to yesterday, with strong storms
possible over northern and eastern portions of the area. Starting
synoptically, the area remains in southwesterly flow aloft as high
pressure remains centered to the south. A shortwave moves through
this flow during the day. The GFS/ECMWF have this wave in northern
Utah around 6am MDT, moving with the flow so that it reaches Johnson
County in the evening (roughly 6pm). This will provide much of the
lift needed for storm development today. Showers and thunderstorms
should begin to develop around noon off the Wind River, southern
Absaroka, and Bighorn Mountains. There could also be some storms
developing in the lower elevations around Johnson and northern
Natrona Counties at this time too. Hi-res models vary on the
coverage of these storms, but have a consensus of them forming
midday. As the mentioned shortwave moves through the area, storms
should develop around the Wind River and/or Bighorn Basins early
afternoon. Again, hi-res models vary a bit in coverage and exact
details, likely due to potential subtle differences in the low level
flow and interactions with the dryline-like feature from yesterday.
These storms then move into the Johnson County area around 5pm,
exiting the area to the east by around 10pm.

Storms have the potential to be strong to severe today, with peak
chances between 3pm and 11pm. Dew points around Johnson County
remain in the mid 50s to around 60F degrees today, lessening to the
south and west. The NAM has precipitable water (PWAT) values in the
150 to 175 percent of normal range around Johnson County this
afternoon and evening. The HRRR has CAPE values in the 1500 to 2000
J/kg range. Shear (1-6km) values of 20 to 30 knots are also forecast
around Johnson County. Putting this together, the same hazards of
yesterday are again possible today: wind gusts over 55 mph, hail 1
inch or larger, and an isolated tornado risk. Like yesterday, the
relatively best conditions do look to remain east and north of the
forecast area. The Storm Prediction Center has the northern and
eastern Bighorn Basin southeast towards Casper in a marginal risk
(level 1 of 5) today, with a slight risk (level 2 of 5) for most of
Johnson County and the northern Bighorn Mountains.

Elevated fire weather conditions also remain today. Dry air is in
place over much of the area, especially across central to
southwestern Wyoming. Afternoon relative humidities drop to around
10 percent, with afternoon wind gusts of at least 20 to 25 mph.
These conditions continue for Sunday and Monday.

Sunday will be much like today. Hot temperatures persist, with
showers and thunderstorm development in the similar northern and
eastern areas. Some of these storms could be strong to severe. On
Monday, the trend continues, with thunderstorms once again possible,
mainly along and east of the Continental Divide as moisture makes it
further into the area. The jet stream will also be in a more
favorable position to support storms. Active weather continues
Tuesday, before lessening Wednesday as high pressure builds in. Hot
temperatures look to return for the end of the next workweek.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1050 PM MDT Fri Jun 13 2025

VFR conditions prevail at all terminals through 06Z/Sunday. Enough
mid-level moisture lingers Saturday to ignite late day convection,
mainly along and north of KJAC-KRIW-KCPR line. Dewpoints
greater than 40F favor a 20-30 percent chance of showers and
storms over the Bighorn Basin, including KCOD and KWRL, between
20Z-24Z/Saturday. A drier sub-cloud layer over the southern
half of the region leads to little more than gusty outflow wind
from isolated late day convection across Fremont, Natrona, and
far southern Sweetwater Counties. Westerly 10-20kt surface wind
expected at many terminals, except KCOD and KWRL, beginning as
early as 19Z/Saturday until around 02Z/Sunday.

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...Wittmann
AVIATION...CNJ/LaVoie