307
FXUS65 KCYS 210812
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
212 AM MDT Fri Aug 21 2026

.KEY MESSAGES...

- Hot temperatures will persist through the end of the work
  week.

- Precipitation chances return by this weekend, with the
  possibility of widespread rain on Saturday.

- Daily shower and storm chances continue Monday through the
  end of the week with slightly above average temperature
  expected until Thursday.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 210 AM MDT Fri Aug 21 2026

Quiet weather early this morning with clearing skies after some
isolated convection late yesterday evening. Surface observations
show pretty light winds across the area with south to southeast
Winds across most of the eastern high plains, and northeast
winds over the far northern Nebraska Panhandle and portions of
east central Wyoming. A weak stationary cold front will remain
in this area for much of the day, and will need to be monitored
for afternoon convection initiation. Otherwise, high resolution
models not showing much in this area today, but do show
scattered rain showers and isolated thunder developing across
southeast Wyoming with activity moving southeast through the
afternoon over the eastern plains. High res models are showing a
little better consistency with this convection over the last
few runs. In addition, models indicate a subtle shortwave
digging southeast across the area on the northeast periphery of
the upper level ridge axis. Believe this feature will be enough
to trigger widely scattered convection...but not totally
convinced we`ll see scattered thunderstorms due to the strength
of the upper level ridge and associated midlevel subsidence.
Increased POP up to 25 percent, but kept a slight chance mention
of thunderstorms for now. SPC as added a marginal and slight
risk of severe weather to the far eastern portion of our western
Nebraska zones. Going to message this lightly since models are
showing poor run to run consistency on deep convection getting
going. Can`t rule this out though with a stationary front in the
area, however. One or two storms may produce gusty winds up to
70 MPH and hail around the size of quarters, mainly east of
Highway 71 over western Nebraska. Pretty hot today with highs in
the 90s pretty much everywhere, with reading in the mid to
upper 90s over the lower elevations of western Nebraska and far
eastern Wyoming.

As we head into the weekend, pretty typical late August weather
pattern over the western United States with strong upper level
high pressure near the four corners region...drifting to the
southeast by Sunday. Southeast Wyoming and western Nebraska will
be in the "ring of fire" around the northern periphery of the
upper level high. All models show a plume of monsoon moisture
(sitting over Arizona/southern Calif at this hour) lifting north
and eventually east around the upper level high on Saturday. In
addition, surface winds will shift into the southeast across the
plains as a potent upper level shortwave moves over the area
Saturday afternoon. NAEFS shows a quick jump in PWATs across the
area with 1.00 inches as far west as Rawlins and Laramie...and
closer to 1.25 to 1.50 across the eastern plains. These values
are around the 97th to 99th percentile for this time of the
year. Ensembles are also starting to hint at the potential of
heavier rainfall across the region, mainly on Saturday.
Increased POP between 40 to 70 percent for scattered to numerous
thunderstorms. Some strong to marginally severe storms are
possible. May need to monitor for excessive rainfall/localized
flooding, especially further south along the I-80 corridor and
lower North Platte River valley. A slight cooling trend
expected this weekend due to plentiful cloud cover and expected
rainfall, with highs in the 80s to low 90s.


&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Issued at 240 PM MDT Thu Aug 20 2026

Monday...Coverage of afternoon and evening showers and thunderstorms
increases somewhat by an increase in pseudo monsoonal moisture and
lowering 700 mb temperatures providing less convective inhibition,
CIN, compared to Sunday. As is this type of pattern, afternoon
convection will be over and near the mountains due to differential
heating and orographic effects, with the activity spreading across
the rest of the forecast area before dissipation by late evening.
Warmer temperatures compared to the previous day due to less cloud
cover and convective coverage.

Tuesday...Similar pattern synoptically to Monday with minor
perturbations in the flow aloft aiding in lift of pseudo monsoonal
moisture to produce widely scattered to scattered afternoon
convection over and near our Snowy, Sierra Madre and northern
Laramie Ranges, with the activity spreading eastward across the rest
of the forecast area in the evening. Some lowering of mid level
temperatures suggests daytime maximum temperatures will be a little
cooler.

Wednesday...The primary change compared to Tuesday, will be a
reinforcement of the ridge aloft axis over Wyoming, inducing a
return to upslope mechanical lift aiding the areal increase of
showers and thunderstorms, especially east of the mountains and
along the I-25 corridor and eastward. Slight warming trend with 700
mb temperatures near 13 Celsius yielding high temperatures in the
80s.

Thursday...Monsoonal moisture becomes a bit more scant with decent
westerly flow aloft and with warm temperatures aloft producing more
convective inhibition, CIN, to limit development. A slight warming
trend continues based on mid level, 700 mb temperature trends.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1125 PM MDT Thu Aug 20 2026

VFR conditions will prevail across all terminals for the duration of
this TAF period. Winds through the night will pose no aviation
hazard as they will primarily be less than 10 knots. Winds ramp up
across all sites with gusts up to 20 knots by 23Z Friday. Winds will
diminish once again by the end of this forecast period to less than
10 knots. Showers and thunderstorms are possible Friday afternoon,
impacting most terminals except KRWL, KCDR, and KAIA. However,
chances remain low and so does confidence, so kept any mention of
activity out of this set of TAFs.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...RZ