216
FXUS65 KCYS 272325
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Thu Aug 27 2026

.KEY MESSAGES...

- Isolated strong to severe thunderstorms are possible over the
  High Plains through the evening hours Thursday.

- Expect hotter weather on Friday with scattered high based
  showers and thunderstorms, bringing a chance for gusty winds.

- Daily chances for afternoon and evening showers and
  thunderstorms continue through at least the middle part of
  next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 215 PM MDT Thu Aug 27 2026

Another potent upper level ridge is building in over the southwest
today, with our area on the periphery. Temperatures are warmer than
yesterday across the area as the ridge amplifies. While clear skies
remain over most of the area, typical diurnal cumulus are building
over the higher terrain of southeast Wyoming, and the Black Hills of
South Dakota. The environment for severe storms is fairly marginal
on the Wyoming side, but more potent as you move eastward into
Nebraska. In Wyoming, MLCAPE is around 500 to 1000 J/kg (higher
right on the state line), with some modest capping still in place,
and deep layer shear around 25 to 35 knots. In Nebraska, we have
MLCAPE pushing 1500 to 2000 J/kg especially in the eastern row of
counties in the Chadron to Sidney corridor. Vertical wind shear
is also stronger, around 35 to 40 knots. The cap is expected to
keep storms fairly isolated today, with lower coverage than the
last few days. However, this may not limit the intensity of
storms that manage to develop. Development will likely be
anchored to the higher terrain, with storms moving generally
southeastward from there. Of particular concern though is the
potential for a right-moving supercell thunderstorm to drop out
of South Dakota. While the environment is not quite as explosive
as last Friday (8/21), there is potential for a similar setup
today. Right-moving supercell vectors are nearly due north to
south, indicating that if a sufficiently strong develops off of
the Black Hills in South Dakota, it could move due south into
the Dawes, Box Butte, and possibly counties further south too.
Overall, today is a conditional threat with a slightly lower
probability of occurrence, but high intensity ceiling. A few
storms may linger into the evening hours, but we should be done
by 11PM to midnight.

The flow aloft will turn southwest Friday as the upper level ridge
axis shifts to the east. A surface trough positioned along the WY/NE
stateline will mark a dryline as westerly to southwesterly flow
spreads into the west, and moist southerly flow remains in place to
the east. This feature will advance eastward through the day,
pushing the most potent environment for strong to severe
thunderstorms off to our east, though we will need to watch for the
dryline progressing slower than modeled, which has occurred
frequently recently. Southwest flow will open the door to a more
favorable monsoon tap. Forecast soundings show a somewhat dry, well-
mixed boundary layer, but plentiful moisture moving in aloft for
tomorrow. We`ll have a little bit of forcing with a vort-max pushing
around the upper level ridge, which should support another round of
scattered showers and thunderstorms. Expect this activity to be high-
based, with a lower overall potential for strong to severe
thunderstorms. However, storms will have the potential to produce
strong, gusty winds. Temperatures will also be quite warm Friday,
with 700-mb temperatures peaking around +14C to +17C. No record
highs are currently forecast, but Cheyenne and Laramie have forecast
highs within about 2 degrees of daily records.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 215 PM MDT Thu Aug 27 2026

.Saturday...The monsoonal moisture tap returns under southwest flow
aloft. With adequate low and mid level moisture, as well as decent
PWAT, precipitable water, values, and a passing shortwave trough
aloft in the afternoon, we anticipate scattered to numerous showers,
and scattered thunderstorms in the afternoon and evening, mainly
south of a Rawlins to Scottsbluff line. Slightly cooler compared to
Friday based on the 700 mb temperature trends.

Sunday...Southwest flow aloft increases in response to a shortwave
trough aloft moving northeastward from eastern Montana southward
into eastern Wyoming. Although PWAT values remain about the same as
on Saturday, afternoon and evening shower and thunderstorm coverage
will be less than Saturday, with more orographic type convection for
our southwest counties in and near the Snowy and Sierra Madre Ranges.
A bit cooler based on mid level temperatures.

Monday...The moisture plume of monsoonal moisture is shunted a bit
further south, over our southern counties, and coverage will be less
with weak shortwave ridging aloft over our counties. Greatest areal
coverage for convection will be south of a Rawlins to Scottsbluff
line. The slight cooling trend continues.

Tuesday...A progressive shortwave trough aloft will pass Monday
night, producing scattered showers and some thunderstorms. Some
drying will occur in the wake of the shortwave trough passage, for
producing a nearly dry forecast for Tuesday afternoon and evening.
700 mb temperatures rise slightly, corresponding to a rise in
surface maximum temperatures.

Wednesday...Brisk southwest flow aloft returns with the monsoonal
moisture stream overhead, and our current scattered afternoon and
evening POPS may need to be increased in the next few model runs.
Temperatures about the same as on Tuesday.

Thursday...Drier air infiltrates the region, thus only isolated to
widely scattered late day showers and thunderstorms expected for the
Snowy and Sierra Madre Ranges, and nearby locations, with dry
conditions elsewhere. 700 mb temperatures suggest little change in
high temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 525 PM MDT Thu Aug 27 2026

VFR conditions will generally prevail across all terminals for
the duration of this TAF period, outside of any showers or
thunderstorms that pass through. The best chances for any
impacts are at KCDR, KAIA, KSNY, and possibly KCYS. If one of
the aforementioned sites gets impacted, expect gusty and erratic
winds along with CIGs lowering and VIS reducing. Due to lower
confidence on timing and location, kept VCTS and/or PROB30
groups in the TAFs. No other aviation threats for the remainder
of the evening into the overnight hours as all the activity
should be out of our CWA. Winds overnight not much of an issue,
but winds ramp back up by 22Z Friday for most terminals with
gusts 20-30 knots.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...RUBIN
AVIATION...RZ