321
FXUS65 KCYS 220522
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1122 PM MDT Fri Aug 21 2026

.KEY MESSAGES...

- 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 131 PM MDT Fri Aug 21 2026

A bit of uncertainty in the forecast for this afternoon and evening
regarding storm chances. Upper-level ridging over the west continues
to shift eastward into Wyoming today. This will produce strong
subsidence which will work to counteract storms. However, model
soundings and mesoanalysis show quite a bit of instability,
especially east of the Laramie Range. Satellite thus far has
been unimpressive, showing flat topped cumulus fields mainly
around Cheyenne and Laramie. A few isolated instances of
vertical growth have been observed, but have quickly fallen
apart due to the presence of MLCIN. Mesoanalysis does have CIN
eroding away within the next few hours, so it is possible that
by late afternoon and evening, storms could develop given the
instability and lift from a weak upper-level disturbance. Most
CAMs aren`t too exited about storms today. The HRRR has been the
most bullish, but also the most uncertain, flip flopping back
and forth between lots of storms and barely any storms. However,
newest runs of the HRRR seem to be more believable, showing
convection developing this evening over the high terrain and
pushing into the panhandle where it strengthens due to higher
instability. If this is the case, a severe thunderstorm or two
could be possible. Both strong winds and large hail cannot be
ruled out in storms with DCAPE over 1000 J/kg and MUCAPE around
1500 J/kg. Any storms that develop will move out of the area by
midnight tonight, however, cannot rule out nocturnal convection
developing in the panhandle after this. Increased moisture into
the area from precipitation as well as weak southeast flow,
could cause low stratus and patchy fog east of the Laramie Range
early Saturday morning.

The forecast for Saturday looks more certain, with greater chances
for precipitation. Another weak shortwave moving through the ridge
will provide the needed lift and monsoon moisture for storms to
develop. Model soundings show decent instability once again, which
could lead to marginally severe storms. Hi-Res guidance shows widely
scattered storms developing during the mid-afternoon and continuing
through the evening hours. Most hazards will be possible in storms,
including heavy rain due to PWATs in the 90th percentile, large
hail, and strong winds. Hi-Res guidance does show lingering showers
across the area Saturday night, however these should not cause
impacts. Similar conditions are expected on Sunday with another
round of scattered storms. PWATs and instability are weaker on
Sunday, so severe storms are unlikely at this time. Due to less
moisture, models are also hinting at lower coverage of storms on
Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 131 PM MDT Fri Aug 21 2026

Monday...Coverage of afternoon and evening showers and thunderstorms
increases somewhat by an increase in 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 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-Friday...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 SUNDAY/...
Issued at 1122 PM MDT Fri Aug 21 2026

A relatively calm night is in store with the possibility of
lower VIS and CIGs across the Nebraska Panhandle with the
additional moisture from Friday`s precipitation and wind
direction. Then, winds ramp up once again across all terminals
by 00Z Sunday with southeasterly to southerly gusts 20 to 25
knots. Another round of showers and thunderstorms look to impact
all sites except KRWL starting around 23Z Saturday, therefore
PROB30 groups have been added. Look for lower VIS along with
gusty and erratic winds in any storm activity if it comes near
or over a terminal. Chances persist towards the tail end of this
forecast period.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM...RUBIN
AVIATION...RZ