643
FXUS65 KCYS 011129
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
Issued by National Weather Service Denver CO
529 AM MDT Tue Sep 1 2026

.KEY MESSAGES...

- Showers ending early this morning with decreasing cloudiness.
  Breezy this afternoon over southeast Wyoming.

- Drying and warming trend expected going into mid to late week
  with growing potential for elevated fire weather conditions,
  mainly north of Interstate 80.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 1109 PM MDT Mon Aug 31 2026

Conditions are relatively quiet this evening across the region
with a few showers mainly across Southeastern Wyoming. This is
being driven by a weak open wave which is providing a source for
DCVA across our region. Current mid-level water vapor imagery
continues to show a plume of monsoonal moisture being advected
north and east over Southeastern Wyoming, which will continue to
push north and east towards the Nebraska Panhandle overnight
into the early morning hours before the bulk of this weak system
lifts to the northeast.

Overnight is when the strongest (albeit fairly weak) forcing
for ascent is expected. Not anticipating too much in the way of
thunderstorm activity as MLCAPE is progged to be <100 J/Kg as a
result of poor low-level lapse rates and surface dewpoints in
the low to mid 40s, but cannot rule out a rumble of thunder with
any of the heavier showers. The main threat overnight will be
localized flash flooding, mainly over portions of Carbon and
Albany Counties where the greatest collocation of total column
moisture and forcing will be, as PWAT values overnight remain
above the 95th percentile. Further, forecast soundings suggest
cloud-layer mean winds of 10-15 knots, so any slow-moving
convective elements could pose a flooding threat. Further east,
the bulk of the forcing from the shortwave trough isnt
temporally collocated with the main moisture surge. This should
limit any hydrological issues primarily east of the I-25
corridor.

Showers are expected to gradually decrease in coverage from
southwest to northeast from late morning through early afternoon
on Tuesday as the wave ejects off to the north and east of our
area. High temperatures Tuesday are expected to be slightly
cooler than Monday, which will ultimately depend on how quickly
showers and clouds depart our area. We can expect westerly winds
to remain breezy, with gusts peaking from 25-30 mph mainly east
of the Laramie Range.

Tuesday night, shortwave mid-level ridging will establish
itself over the Northern Great Plains with a continuing trend of
decreasing cloud cover. Overnight temperatures will remain
quite mild, especially north of the Pine Ridge where 10-25 knot
southerly low-level flow will help to moderate temperatures
thanks to downsloping.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 256 PM MDT Mon Aug 31 2026

Wednesday...Brisk southwest flow aloft prevails. Low and mid
level moisture availability looks scant, thus POPS near zero and
negligible. Based on the low and mid level gradients, it looks
like it will be windy.

Thursday...Similar day to Wednesday with rather strong and dry
southwest flow aloft and decent and deep unidirectional
southwest flow for a windy and dry day.

Friday...The flow backs to south southwest and weakens
somewhat, with minor influx of pseudo monsoonal mid level
moisture, though confidence in shower and thunderstorms
development is negligible thus will keep it dry.

Saturday...Looks like a pseudo moisture tap will emanate up
from the Four Corners with an uptick in PWAT, Precipitable Water
Content, noted, thus expect isolated to scattered afternoon
showers and thunderstorms for our Snowy and Sierra Madre Ranges,
with the activity spreading northeastward and remaining mostly
west of I-25 in the evening.

Sunday...Once again, the rather moist southwest flow will tap
pseudo monsoonal moisture and diurnal heating and orographic
effects will help produce scattered showers and thunderstorms in
the afternoon for locations over and near the Snowy and Sierra
Madre, and northern Laramie Ranges, with the convection
spreading across the remainder of southeast Wyoming and western
Nebraska in the evening.

Monday...Ridging aloft over the Central Plains states bulges
westward across our counties, though with adequate low and mid
level moisture, we still anticipate scattered afternoon and
evening showers and thunderstorms.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 520 AM MDT Tue Sep 1 2026

Upper level trough axis will lift northward this morning across
the eastern plains. Light to occasionally moderate rain shower
activity will end by 17z, with a few isolated thunder showers
possible late this afternoon and this evening.

HAZARD/WEATHER TRENDS: VFR conditions will prevail over the
next 24 hours with brief MVFR VIS in the heavier showers near
KCDR and KAIA. Mostly dry for the remainder of the day, but
cannot rule out a few brief thunder showers near KSNY, KCDR,
and KRWL. However, not confident enough to put in the TAF at
this time with minimal coverage.

Otherwise, breezy conditions expected at KRWL, KLAR, and KCYS
after 15z this morning with gusts around 35 knots possible at
KRWL. Winds should subside between 00z to 03z this evening.


&&

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

&&

$$

SHORT TERM...WFOCYS
LONG TERM...WFOCYS
AVIATION...WFOCYS