189
FXUS65 KCYS 190450
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1050 PM MDT Mon Aug 18 2025

.KEY MESSAGES...

- Scattered thunderstorms with isolated large hail or strong
  winds possible will taper off through the evening.

- Hot temperatures with more limited thunderstorm chances are
  expected Tuesday through Thursday.

- A cold front late in the week will decrease temperatures and
  increase thunderstorm chances heading into the weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 144 PM MDT Mon Aug 18 2025

Showers and thunderstorms are developing and building across
southeastern Wyoming as models aloft indicate some energy clipping
eastern portions of the CWA. The threat of storms will expand into
portions of the Nebraska panhandle this afternoon into the early
evening hours. The best instability and the greatest threat of
severe weather will remain across the southern counties of the
Nebraska panhandle. This convective weather will be driven by modest
instability, but may be limited by poor low level moisture. Forecast
soundings indicate that these storms will be capable of producing
strong gusty winds along with the possibility of pea to nickel sized
hail, primarily along the southern counties of the Nebraska
panhandle as indicated by hi-res models.

Ridging aloft will strengthen over the next few days as high
pressure over the Four-Corners region dominates weather conditions
across the CWA. Rain and thunderstorm chances decrease as
temperatures increase a few degrees each day through at least mid-
week. With the building ridge, temperatures rise but it comes with a
decrease in moisture, this may bring an enhanced risk of fire
weather concerns for portions of our CWA as well. One thing that may
mitigate the fire weather concern is a weak gradient, resulting in
weaker winds across the region. We will continue to monitor this
evolving pattern over the several days for any areas that may need
watches or warnings.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 144 PM MDT Mon Aug 18 2025

The latest heat wave will peak Wednesday and Thursday across the
area as the powerful ridge amplifies over the Four Corners region.
700-mb temperatures will crest around +16 to +18C between Wednesday
afternoon and Thursday afternoon per the NAEFS average, which is
near the 99th percentile of climatology. Record highs are most
likely at Laramie and Rawlins, where boundary layer moisture is
expected to be considerably lower with deep inverted-v soundings in
place. East of the Laramie Range, low-level moisture is expected to
be somewhat high, at least relative to typical heat waves of this
magnitude. This will be thanks to southeast to south winds on
Wednesday, turning northeast on Thursday, but maintaining moisture
over the High Plains. With shallower mixed layers, daily record
highs are less likely compared to areas further west, but we can
still expect widespread 90s with a shot at 100F. For Wednesday, the
middle to upper atmosphere will remain quite dry which should
suppress afternoon convective activity, but the boundary layer
moisture may be enough to get isolated low-topped showers and
thunderstorms going, particularly near and adjacent to the higher
terrain. By Thursday, a shortwave trough riding over the top of the
ridge will pull better moisture out of the monsoon with it, and
increase mid to upper level humidity. This should mix down and
increase dewpoints west of the Laramie range, while those to the
east will see dewpoints similar or slightly lower than Wednesday.
Expect to see shower and thunderstorm covering increase for Thursday.

A cold front is expected to pass through the High Plains on
Thursday, bringing a notable pattern chance for Friday into the
weekend. The overall synoptic weather pattern will be characterized
by a powerful Four Corners ridge retreating slightly south and
westward, and frequent shortwave troughs diving over our area on the
northwest flank of the ridge. A persistent surface high pressure
over the northern Plains will keep a cooler and wetter airmass in
the lower atmosphere pushed up against the mountains, while good to
excellent monsoon moisture will continue to pump around the upper
level high and into our area. The NAEFS average shows precipitable
water around the 90th percentile of climatology beginning late
Thursday and continuing through the rest of the forecast period.
Expect scattered to numerous showers and thunderstorms beginning
Friday afternoon and continuing through at least Monday. It`s too
early to get into the details of the severe potential and storm
mode, but the overall pattern suggests at least a marginal severe
potential each afternoon through this period.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1050 PM MDT Mon Aug 18 2025

Period of quiet weather expected to begin Tuesday as a strengthening
upper level high pressure over Colorado dominates the weather
pattern across the Front Range.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24
hours. After a period of gusty southerly winds for KCYS and KLAR,
winds should become light out of the south or southeast. Expect this
to continue through Tuesday with gusts up to 20 knots. Can`t rule
out a few showers or thunderstorms for the southeast Wyoming
terminals, but due to limited coverage (very isolated), kept out of
those TAFs for now.

&&

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

&&

$$

SHORT TERM...RZ
LONG TERM...MN
AVIATION...TJT