196
FXUS65 KCYS 172121
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
321 PM MDT Sun Aug 17 2025

.KEY MESSAGES...

- Widely scattered showers and thunderstorms will continue
  through the evening hours, with gusty winds and isolated hail
  possible. Another round of isolated storms is expected
  Monday.

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

- A cold front late in the week should bring back rainfall
  chances and cooler temperatures leading into the weekend.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 320 PM MDT Sun Aug 17 2025

Widely scattered showers and thunderstorms have developed over the
area once again this afternoon as a weak vort-max moves across
Central Wyoming. GOES water vapor imagery shows an area of dry air
in the upper troposphere moving in from the southwest, splitting the
better moisture both to our north and south. Soundings suggest that
decent moisture is still present in roughly the 500 to 700-mb layer,
with drier air moving in above this. This is sufficient to support
about 500 to 1000 J/kg SBCAPE across much of southeast Wyoming, but
most of the storms that have developed so far are fairly low topped.
A diffuse dryline is positioned somewhere in the wester Nebraska
panhandle, and instability begins to increase heading east with
SBCAPE pushing 2000 J/kg around the Chadron area. Shear is
fairly modest once again, but once storms move into the more
unstable environment generally along/east of a Harrison to
Alliance line, we may see some isolated stronger winds or larger
hail. Further west, the dry-ish boundary layer will yield the
potential for gusty winds, but so far, these are only producing
gusts to around 45 mph. Thunderstorm activity should be mostly
concluded by 8PM, but a few lingering showers will be possible
in our northern zones until about midnight, and then near Sidney
into Monday morning.

The powerful ridge over the southern Plains will begin to amplify
and retrograde on Monday, locking in fairly hot temperatures through
much of the week ahead. Expect highs similar to today or perhaps a
few degrees warmer, reaching generally the upper 80s to 90s. Weak
upslope flow will keep decent low-level moisture and modest vertical
wind shear in place over the Nebraska panhandle for Monday, leading
to slightly more potent soundings. Overall thunderstorm coverage is
still expected to be isolated (even more so than yesterday and
today), but storms that develop may have a better chance of becoming
strong to severe. The best forcing appears to be along the I-80
corridor east of Cheyenne towards Sidney with model guidance showing
modest overrunning flow in this area.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 320 PM MDT Sun Aug 17 2025

Tuesday through Thursday morning, the upper level ridge becomes
rooted into the four corners region making us hot and dry for
potential fire weather concerns. 700mb temps returns to that 20C
threshold allowing for surface temperatures to reach 90 to 100F in
the lower elevations while the higher elevations will be in the 80
to 90F range. While RH values will be in the teens and single digits
the winds will be calm to a subtle breeze but not strong enough to
for any fire weather products to be issued. Fires will be easily
started nonetheless as fuels remain cured and primed in most
locations. Thursday currently appears to the hottest day however
there is a cold front that may prevent some of those higher
temperatures depending on timing. The cold front does have some
uncertainty as the global models have different timings for the
arrival of the cold front. This cold front also may be the start of
our precipitation chances for the week as a large low pressure
system is progged to move across/along the Canadian border and
flattening our ridge. Friday and into the weekend precipitation
chances increase as more moisture advects into the region by a low
pressure system moving across/along the Canadian border. NAEFS shows
PWAT values increasing, which in turn will resurrect any
precipitation chances by any shortwave moving through the
region.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1138 AM MDT Sun Aug 17 2025

Another weak shortwave is going to move through this afternoon
and evening. While storm development may start in the higher
elevations, it doesn`t appear like any of the Wyoming terminals
will be affected. KBFF, KCDR, and KAIA may be the only ones
affected by any thunderstorms and showers this evening. All
storm development looks to be done by 04z. Tomorrow winds will
be light and possibly variable as the upper ridge pushes back
over the Intermountain west.

&&

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

&&

$$

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