323
FXUS65 KCYS 290428
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1028 PM MDT Thu Aug 28 2025

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms will continue
  through the evening hours today. Isolated torrential rainfall
  and hail are the primary hazards.

- Widely scattered thunderstorms are expected again during the
 PM hours on Friday and Saturday.

- Warming trend starts Sunday onwards, with fire weather
  concerns slowly creeping up to start the work week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 300 PM MDT Thu Aug 28 2025

Thunderstorm activity got off to an early start this afternoon. GOES
water vapor satellite imagery shows our area sandwiched between a
healthy plume of monsoon moisture streaming in from the southwest,
and lingering moisture associated with the very disorganized upper
level low over the northern Rockies. The feature passing to our
north is helping to produce modest overrunning warm air advection,
strongest generally along a Casper to Pine Bluffs line. While
convective parameters are fairly marginal, the forcing appears to be
enough to kick off scattered to numerous thunderstorms, with
isolated strong to severe storms. The primary hazards so far are
torrential rainfall and small to marginally severe hail, but an
isolated landspout and/or damaging wind gust cannot be ruled out.
Soundings are extremely moist once again, but we have a little bit
of drier air filtering in above 500-mb that may be helping to
produce a little more hail and lightning compared to yesterday. The
isolated severe threat should be mainly confined to the areas where
the forcing is stronger, which weakens quickly past far western
Nebraska. Expect this activity to grow upscale for few hours, and
then begin a slow down trend through the evening, with most activity
concluded by 9PM aside from lingering late evening convection in
Converse/Niobrara counties.

Winds will gain a light westerly component overnight in southeast
Wyoming, which will keep the low cloud/fog confined to mainly the
Nebraska panhandle, but this could spread into northern Goshen and
Niobrara counties too. The airmass in the westerly flow will still be
fairly moist though, so this won`t exactly be a well defined
dryline. For Friday, the disorganized upper level low will continue
to linger near the area as it continues its very slow progression
over the op of the weak southwest CONUS ridge. Models show a very
messy 500-mb vorticity pattern, with numerous vort-maxes floating
around the area. This will provide some forcing, but overall it
looks weaker than today which should decrease thunderstorm coverage.
Storms should be more in the widely scattered category. Dry air
should reduce the chance for storms in northern Carbon and Albany
counties, but most of the rest of the area will be fair game.
Convective parameters are marginal once again but isolated severe
hail and/or wind cannot be entirely ruled out. Friday also looks
like the warmest day of the week, thanks to more widespread sunshine
compared to the last week or so. A reinforcing cool front will slip
across the High Plains Friday night, possibly enhancing some late
evening thunderstorm activity and bringing in another round of
morning low clouds and/or fog.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 300 PM MDT Thu Aug 28 2025

Northwest flow continues through Saturday continuing our
chances for afternoon and evening. Sunday, the upper level ridge
starts to build back over the intermountain west. This will
slowly start to decrease the moisture over the region. A weak
disturbance does give us a slight chance for an isolated shower
but the probability looks low enough to not include in the
grids. Monday and Tuesday looks to keep us dry as the ridge
shift back over the Intermountain west as a low pressure system
enters the Pacific Northwest. Cluster analysis does show some
uncertainty as to the timing of the Low pressure system which
may break down the ridge by Tuesday afternoon but NBM looks to
side more with the GEFS and paints a 20 percent chance of
showers. However, if the Ridge doesn`t break down until Tuesday
evening as 70 percent of the Grand Ensemble members (GEFS, Euro,
Canadian GEPS) then we should stay dry until Wednesday.
Wednesday, The Intermountain West becomes sandwiched between an
upper level ridge and Low pressure system near the Great Lakes
Region. This will give us gusty winds for the rest of the week
and afternoon precipitation chances until at least the end of
the work week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1020 PM MDT Thu Aug 28 2025

West flow aloft will continue.

Wyoming TAFS...Scattered to broken clouds from 7000 to
10000 feet will prevail. Winds will gust to 23 knots from
15Z to 17Z, to 00Z.

Nebraska TAFS...Scattered to broken clouds near 10000 feet will
prevail. Ceilings will range from 800 to 1500 feet at Alliance,
Scottsbluff and Sidney with areas of fog reducing visibilities
to 3 to 4 miles until 15Z Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...MM
AVIATION...RUBIN