172
FXUS65 KRIW 080044
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
644 PM MDT Sun Jun 7 2026

.KEY MESSAGES...

- Showers and thunderstorms have started to wane this evening,
  with isolated showers and storms remaining possible from
  Sweetwater County to Natrona County through 10PM.

- A cold front will progress southward this evening, with gusts
  of 45 to 55 mph possible across Johnson County, northern
  portions of the Bighorn Basin, and the Wind River Basin in
  the wake of the front. Temperatures will be 10 to 15 degrees
  cooler tonight as a result.

- Breezy southwest winds with gusts of 25 to 35 mph will return
  across areas west of the Divide Monday. Elevated to critical
  fire weather conditions will return to central and southern
  portions of the forecast area.

- A strong cold front will impact the region starting Tuesday,
  with the possibility for strong to high winds at times over
  wind prone locations. Cooler temperatures will arrive over
  western portions Tuesday, spreading to the rest of the
  forecast area on Wednesday.

&&

.UPDATE...
Issued at 1242 PM MDT Sun Jun 7 2026

Thunderstorm coverage is expected to increase over the next few
hours as instability builds. This will be focused mostly east
of the Divide where SBCAPE values will reach 500-1000 J/kg. The
strongest storms are still expected in the eastern Bighorn Basin
and across Johnson County where instability and shear (30-40
knots bulk) will be maximized. A narrower band of instability
should also develop farther south, extending through Sweetwater
County within a relatively more moist airmass. Stronger storms
today will be capable of occasional large hail and strong wind
gusts of 60 to 70 mph. Convection will wane by late evening,
with most of this activity to our east by midnight.

&&

.DISCUSSION...
Issued at 200 AM MDT Sun Jun 7 2026

WV imagery currently shows the deep upper level trough across
the Pacific northwest with the PFJ pushing cyclonically around
it with a positive tilt just to the west of the state. IR shows
the cooler cloud tops over eastern Idaho into central Montana
that will slowly push east into the CWA by Sunday morning
expanding throughout the day. Some light rain showers across
the west that will dissipate by sunrise with another round of
scattered thunderstorms expected to develop by late morning
across the Bighorn Basin. Gusty outflow winds expected with
this occurrence but severe weather is not expected through
early afternoon. As this pushes northeast by mid afternoon
~3-4PM, another area of development expected to off the leeward
side of the Absarokas by 4-5PM pushing across the north central
portions of the basin expanding to the Bighorns. These look to
form more of a line across the pre-frontal troughing with winds
again the main concern with possible severe thresholds being
met.

Attention turns to the more discrete cells come 6PM onward
towards sunset as the weak storms across Sweetwater County push
across Natrona into Johnson County. This will be when hail could
be more of a threat before quickly pushing northeast out of the
CWA before sunset around 8PM. With the ample surface convergence
and modest lapse rates, larger hail possible with moderate
confidence for severe thresholds up to a quarter. CAPE values
over 1500 J/kg ahead of FROPA will be conducive to this
occurrence with low level shear aiding in hail growth over 30
knots. The more upscale growth will occur after sunset and
northeast of the CWA into western South Dakota. These strong to
severe storms for hail potential will be short lived for our CWA
with the time frame of concern between 6-8PM. Otherwise, any
other stronger storms for the eastern Bighorn Basin across the
Bighorns and northern Natrona County will be more of a wind
threat but below severe thresholds at this point in time. A long
Sunday night looks to be in store severe wise for Rapid City and
point north and east into Monday morning.

Beyond the storm activity, expect FROPA to occur north to south
by late afternoon and into the late evening hours. Warm
temperatures ahead of the front will still give way to above
average temperatures but not record breaking as it was Saturday
due to the increased cloud coverage with this first shortwave.
Fire weather conditions expected to be near critical to critical
ahead of FROPA with gusty southwest winds to develop by mid to
late Sunday morning, strongest across Sweetwater to Natrona
Counties for the wind corridor up to 30 to 40 mph likely. Winds
shift with more of a northern component behind FROPA pushing
through the CWA after midnight and into early Monday morning
diminishing by sunrise.

Continued active pattern with the aforementioned L/W trough to
the northwest with a multitude of shortwaves through Thursday.
With cooler temperatures, severe weather is not expected but
expect a daily afternoon/evening dose of scattered storm
activity along with elevated fire weather danger as well. The
coolest day of the week looks to be Wednesday with a stronger
cold front with the the more widely scattered rainfall activity
expected. Beyond Thursday, the low finally exits to the east as
increased convergence aloft and upper level ridging builds back
in for Friday and into next weekend with a warming and dry
trend expected.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 508 PM MDT Sun Jun 7 2026

Gusty winds are forecast at the start of the TAF period, with
frequent gusts of 25kts to 35kts. Wind gusts closer to 40kts are
possible as well, especially at KCPR. Winds begin weakening between
02Z and 07Z and become more northwesterly to northeasterly, behind a
cold front, during this timeframe as well. Expect winds to be 12kts
or less overnight. Gusty 20kt to 30kt winds return to all terminals
except KRIW and KCOD between 18Z and 21Z Monday. There is a 30
percent chance for showers and thunderstorms until 03Z at KRKS and
until 06Z at KCPR. Gusty winds could accompany any showers and
thunderstorms.

There is a 30 percent chance of low clouds moving into KCPR between
06Z and 14Z Monday, but did not have enough confidence to go with
MVFR ceilings. Another weak boundary looks to trek across the state
between 10Z and 16Z Monday. Confidence in this bringing any light
rain to the terminals is between 5% and 20% so did not include in
any TAF at this time.

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

&&

.FIRE WEATHER...
Issued at 200 AM MDT Sun Jun 7 2026

Near critical to critical fire weather conditions expected for
Sunday afternoon and evening due to gusty southwest winds up to
30 to 40 mph and low relative humidity values down to 8 to 12%.
Although most fire weather zones are green for fuels (outside of
much of Natrona County), fire weather will be of concern for
Sunday. Scattered thunderstorms are expected from eastern
Bighorn Basin/Fremont County to Natrona/Johnson Counties for
late Sunday afternoon and early evening. Gusty outflow winds
possible up to 50-60 mph with some of the stronger storms.
Active weather pattern continues into much of the work week,
but with not as warm temperatures giving way to higher humidity
values and only elevated fire weather concerns after Sunday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for WYZ280.

&&

$$

UPDATE...Myers
DISCUSSION...Lowe
AVIATION...Gerhardt/Rowe
FIRE WEATHER...Lowe