Shell, Wyoming Weather Forecast Discussion

449
FXUS65 KRIW 111823
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
1223 PM MDT Thu Sep 11 2025
.KEY MESSAGES...
- Showers and thunderstorms possible through the evening across
  the area. Gusty outflow winds are the main hazards, though
  small hail is possible.
- Chances for showers and thunderstorms continue into Friday and
  Saturday, with cooler temperatures as well.
&&
.UPDATE...
Issued at 1221 PM MDT Thu Sep 11 2025
Forecast focus today is on the showers and storms. Have updated the
forecast with the latest hi-res model data. Have also included at
least a 15 percent chance for the entire area to account for the
differences between models and individual model runs. The main
hazard from any storm is outflow winds. Jet stream location will
help support some stronger storms this afternoon and evening. The
HRRR has 50+ mph winds this afternoon associated with storm
outflows, from around Rock Springs to Casper. Outflows will also be
likely elsewhere across the area, with gusts more in the 30 to 40
mph range. Outside these storms, synoptic winds bring a gusty south
to southwest wind through early evening. The threat of storms
diminishes around 02Z (8pm MDT).
&&
.SYNOPSIS...
Issued at 304 AM MDT Thu Sep 11 2025
A trough continues to dig across the western CONUS this morning and
will gradually shift east into the Great Basin. This will be the
next weather maker, bringing chances for showers and thunderstorms
through the remainder of the week into the weekend. The overall
trend has been towards a more unorganized system, which would lead
to less precipitation and lower impacts across much of the CWA.
A low will develop in the northern portion of the trough over
MT and ID with a second low attempting to develop farther to the
south. As a result the bulk of the impacts will remain to the
north and south of the CWA. Embedded shortwaves associated with
the trough will move through the region bringing chances for
precipitation in the form of daily showers and thunderstorms.
Long range models indicate the chance for another disturbance
arriving for the first half of next week. As of this morning
impacts would be mainly confined to northern and western WY.
&&
.DISCUSSION...
Issued at 304 AM MDT Thu Sep 11 2025
Showers and an isolated thunderstorm or two are moving across the
state this morning. Conditions should dry out by the late morning
with partly to mostly sunny skies expected through the mid
afternoon. Southwesterly flow increases across the region today as a
deep trough over the western CONUS begins to near. 700 MB winds of
30 to 40 knots move into the region which will lead to gusty surface
winds of 25 to 35 mph throughout the afternoon Thursday.
Temperatures today remain above normal east of the Divide with highs
in the low to mid 80s. Locations west of the Divide look to see more
seasonable temperatures in the low 70s as a result of the nearing
trough. Increasing southwesterly flow will usher in drier air
leading to dewpoint depressions of 45 to nearly 50 degrees in some
locations. A second round of showers and thunderstorms looks to
develop during the afternoon and evening. Due to the overall dryness
of the atmosphere many locations will see little to no moisture
reach the surface. The concern as a result of this dryness will be
strong gusty outflow winds of 40 to 50 mph nearby any showers and
thunderstorms as they develop and collapse. Elevated to near
critical fire weather conditions will be possible in portions
of the state today. The only limiting factor for Red Flag
Warnings are RH values slightly above 15%. So while not fire
weather highlights will be issued, favorable fire weather
conditions will be possible especially east of the Divide.
Friday will start to see conditions shift as the trough axis nears
the area. Cooler temperatures slightly below normal are forecast
west of the Divide with highs in the upper 60s to low 70s. East of
the Divide remains warm but with temperatures beginning to gradually
cool as highs range in the upper 70s to low 80s. Winds increase once
again during the afternoon but with gusts mainly around 20 mph. The
atmosphere remains dry but not to the same extent as Thursday with
lesser dewpoint depressions of only 30 to 40 degrees. Showers and
thunderstorms will be possible once again starting in the early
afternoon and spreading to the northeast into the evening. Coverage
will be more widespread compared to Thursday but the dryness may
limit moisture from reaching the surface in some areas. This dryness
may once again lead to some gusty outflow winds nearby any showers
or storms. Elevated fire weather conditions look possible at times
Friday with lesser concerns due to weaker winds and higher min RH
values around 20 to 30%.
The trough axis enters the area by Saturday with shortwaves moving
across the state through the weekend. This will lead to continued
chances for showers and thunderstorms Saturday through Sunday
morning. Temperatures will continue to cool over the weekend with
highs west of the Divide in the mid 60s and highs east of the Divide
in the mid to upper 70s. Long range models show a brief lull in
activity for most of Sunday before the next disturbance moves in
from the PACNW. The exact impacts from this disturbance remains
unknown as models do not have good agreement regarding the track.
Differing tracks of this disturbance will lead to differing impacts.
A better idea of what to expect should begin to develop by the end
of the week.
&&
.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1141 AM MDT Thu Sep 11 2025
The predominant aviation concern will continue to be convection at
or near terminals. Any showers or thunderstorms will be capable of
producing strong outflow wind gusts, perhaps as high as 40 to 50
knots given the large temperature - dewpoint depressions today. This
activity is expected to become more widespread early this afternoon,
moving northeastward through the evening. All terminals now carry
either a TEMPO or PROB30 group to account for this today. Convection
will mostly come to an end after sunset, though continued
unsettled conditions will keep some showers in the area
overnight. The best chance for this will be at KBPI, KCOD, and
KPNA.
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.
&&
$$
UPDATE...Wittmann
SYNOPSIS...Dziewaltowski
DISCUSSION...Dziewaltowski
AVIATION...Myers

NWS RIW Office Area Forecast Discussion