614
FXUS65 KRIW 141042
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
442 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. Dewpoints 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 /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 430 AM MDT Sat Jun 14 2025

Mostly SKC skies this morning, with VFR conditions expected to prevail
at all terminals through the TAF period. However, LIFR/IFR
clouds have developed near KCPR and northern Natrona County.
These clouds should lift/dissipate around 15Z/16Z. Enough mid-
level moisture lingers today to ignite late day convection,
mainly along and north of KJAC- KRIW- KCPR line and confined
mostly east of the Divide. 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. These
showers and storms will progress into Johnson County and exit
the forecast area after 03Z. Large hail and strong winds will be
possible with those storms. 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...LaVoie/CNJ