955
FXUS65 KCYS 160538
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1138 PM MDT Wed Oct 15 2025

.KEY MESSAGES...

- A storm system will move through the area today and Thursday,
  first bringing showers and thunderstorms, followed by
  mountain snow and strong winds across the wind prone areas of
  southeast Wyoming.

- A few of the thunderstorms this afternoon may become strong to
  marginally severe, of which they may produce hail and gusty
  winds along with heavy rainfall.

- Clipper system on Saturday brings another round of strong
  winds and some regional precipitation.

&&

.MESOSCALE...
Issued at 227 PM MDT Wed Oct 15 2025

Afternoon GOES satellite imagery reveals a thick blanket of
persistent stratus cloud cover over much of east-central
Wyoming east of the Laramie Range, as well as the northern and
central Nebraska Panhandle. This stratus cloud cover is a
visible sign of robust CIN/capping which remains in place over
this region. Farther south across Laramie County Wyoming as
well as the Kimball to Sidney corridor in the southwest NE
panhandle...surface heating and mixing has eroded the morning
fog/cloud layer with around 1000 J/kg of SBCAPE present per RAP
mesoanalysis fields. To the west of the Laramie range, dewpoint
depressions are much higher with some high- based convective
cloud cover developing over the Sierra Madre and Snowy ranges.

As we move through the later afternoon hours, a deep trough will dig
through the Great Basin and Four Corners region. Ahead of this
system...favorable dynamics including divergence aloft, a potent mid-
level jet streak with 500mb winds in the 50-70kt range, and rapidly
cooling mid-level temperatures leading to increasing lapse rates
will all combine to place a rather favorable parameter space for
strong thunderstorms over southeast Wyoming and western Nebraska.
The limiting factor in the thunderstorm forecast today will continue
to be instability - or rather a lack thereof. While clouds have
cleared along the I-80 corridor east of the Laramie range and
surface dewpoints are in the mid to even upper-50s, air temperatures
still need about 5-10 degrees of warming to support robust
convective initiation. Given the large amount of ML CIN still
in place, it is likely that we will have to rely on convective
initiation in the mountains to the west, as well as
thunderstorms initiating along a developing Denver Cyclone
boundary in northeast Colorado. CAM guidance and HREF ensemble
members have been more consistent in CI this afternoon and
evening in these locations, with storms moving north out of
Colorado into southern Wyoming and southwest Nebraska in the
23-01z timeframe.

While instability profiles leave much to be desired, the kinematic
profile does support multicell to supercell thunderstorm mode with
any convection that can maintain itself in the Cheyenne CWA east of
the Laramie Range this evening. Long, curving hodographs are present
by 0z as the southeasterly low-level jet intensifies underneath
strong southwesterly flow aloft. Effective bulk shear over 60 knots
and 0-3km SRH in the 150-300 range as seen on both the NAM Nest and
recent HRRR runs also support rotating updrafts with threats for
hail over 1" in diameter and gusty outflow winds. If surface
temperatures were a few degrees warmer, a tornado threat would also
be present. Ultimately however, the most likely scenario this
afternoon and evening will be for surface-based thunderstorms to
quickly become elevated and lose their punch north of the I-80
corridor given capping remaining in place. As stronger forcing moves
in aloft after 0z, another round of stronger showers and
thunderstorms will likely form over the Laramie range and move
through east-central Wyoming. These storms, likely elevated on top
of the stable boundary layer, could also bring a wind and hail
threat from Wheatland through Torrington and Chadron through
around 6z tonight.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 406 PM MDT Wed Oct 15 2025

Active weather expected through Thursday as a a surface low and
attendant frontal boundaries make their way through our region
while aloft a deep low lifts up across central Wyoming bringing
a strong jet across our region through early Friday. As
discussed in the mesoscale section, this will promote the
potential for some stronger to severe thunderstorms lifting from
our south to north, but the environment is struggling across
our more northern zones thanks to the stubborn low stratus deck
in this region along and head of the slow lifting warm front.
For more information through this evening, see the mesoscale
section. As thunderstorms continue into the evening we may see
a lingering risk for some stronger activity before waning and
becoming more general shower and thunderstorm activity that will
continue into Thursday as the cold front associated with this
system passes across our region by the morning hours. Post-
frontal precipitation may continue into Thursday but should be
general shower and thunderstorm activity in nature, alongside
some mountain snow for the Sierra-Madre and Snowy ranges.
Overall accumulations look to remain light to moderate near the
peaks, but should remain low enough to preclude a need for
winter products for these zones. Finally, the aforementioned jet
and tightened surface pressure gradient should enhance our
winds, with stronger gusts starting Thursday afternoon and
continuing into Friday afternoon. Currently a high wind watch is
out for later Thursday through early Friday afternoon, but this
could be extended to start as early as the beginning of the
afternoon tomorrow.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 406 PM MDT Wed Oct 15 2025

As the trough that brought about our short term weather departs,
a secondary clipper trough from our northwest will move across
the region Friday into Saturday. While moisture may not be as
abundant as it currently is, a few showers and mountain snow
showers may be possible. This clipper is bringing in some cooler
air, and could even bring snow levels lower than expected with a
quick glancing hit of some lower elevation snow, but it would be
brief and not expected to accumulate of course. Meanwhile the
jet associated with this feature could once again fuel another
round of strong winds on Saturday, bringing high wind gusts to
our wind prone locations. Sunday a transient ridge will help to
clear us out and briefly warm us back into the 60`s to low 70`s,
but a deep Pacific trough will bring another round of rain and
breezy winds Monday into Tuesday of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1138 PM MDT Wed Oct 15 2025

A few lingering showers continue overnight with the chance for a few
rumbles of thunder, mainly out by KRWL. Low stratus will likely
continue to push south throughout the night, affecting terminals in
the Nebraska panhandle with low CIGs. Low CIGs will lead to MVFR
and/or IFR conditions. Fog and dense fog will also be possible which
will limit visibility. Fog and low stratus will lift throughout the
morning, improving conditions across the area.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from late Thursday night through Friday
     afternoon for WYZ106-107-110-116-117.
NE...None.

&&

$$

MESOSCALE...MAC
SHORT TERM...CG
LONG TERM...CG
AVIATION...SF