428
FXUS65 KCYS 182101
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
301 PM MDT Fri Sep 18 2026

.KEY MESSAGES...

- Active with scattered to numerous showers and thunderstorms
  into the weekend. Strong to marginally severe thunderstorms
  may return to the area as a potent Pacific storm system moves
  into Wyoming Saturday and Saturday night.

- Active weather with cooler temperatures expected for much of
  the upcoming week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 259 PM MDT Fri Sep 18 2026

An active evening and weekend is in store for us. The upper level
low is further south than what the models originally had when
comparing current satellite Water vapor to global model outputs. The
position of the upper level low will really be important over the
next 48 to 72 hours. There is a low amplitude ridge over the
southern plains that if the central pressure shifts a little west
will slow down this low much like a tall speed bump at a car show in
a Walmart parking lot. If that occurs, expect heavy rain showers and
borderline severe to severe thunderstorms over the weekend. Judging
by its current speed and anticipated trajectory this low is more
likely to straddle the Colorado/Wyoming giving us decent widespread
rainfall but a little bit less likely on the severe aspect. Hi-res
guidance puts about 500 to 1000 joules east of I-25. There are some
pockets of 2,000 joules which may be over done with the okay lapse
rates between 6.5 to 7.0c and 700mb temperatures between 8 and 10C.
Some cold air will be following this low dropping 700mb temperatures
from 10C to 6C leafing to high temperatures slowly dropping through
the weekend. By Sunday the high temperatures are in the 60`s and the
forecast area may be a little too cool for severe weather but heavy
rainfall looks to be a daily afternoon and evening occurrence.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Issued at 259 PM MDT Fri Sep 18 2026

Forecast for next week looks to remain largely the same from day
to day under weak pressure gradients aloft with a few chances
for some scattered precipitation, but otherwise a cool start to
the weak with a slow and steady warming trend through the
remainder of. Upper level pattern will consist of weak ridging
trying to build in on Monday, but this will be overtaken by a
weak low lifting up from California and slowly progressing
across the region through the end of the forecast period. At the
surface, Monday will see our forecast region in a post-frontal
environment, with a weak boundary then sitting across the WY/NE
border area and then lifting east-northeast as a warm front into
the later days of the week. Under this pattern Monday will be
the coolest day of the forecast period as widespread highs
generally sit in the 60`s to right around 70 in the warmest
spots. Increasing warmth then expected as warmer air from the
southwest moves across the region, but don`t expect a crazy
warmup as we increase only 1-3 degrees each day, keeping the
region mostly in the 70`s through the week until Thursday when a
few more 80`s may finally begin popping up. A brief blip of
moisture may produce increased chances of showers and storms on
Tuesday as the California low lifts up, but without a stout
forcing mechanism don`t expect much outside of general showers
and thunderstorms and coverage isolated to scattered at best.
Otherwise, a few isolated showers or storms possible each day as
well with nothing impactful expected.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1139 AM MDT Fri Sep 18 2026

A mix of flight categories are expected over the next 24 hours
due to passing showers and thunderstorms followed by lowering
ceilings in Nebraska. Periods of MVFR are possible with the
strongest precipitation, with late night and early morning CIGs
then becoming IFR to LIFR for all Nebraska sites except KBFF.
Widespread CIGs outside of this will be generally mid level with
precipitation. Best chances for thunderstorms between 21-03Z,
starting in Wyoming and continuing into Nebraska. Winds
generally 10 knots or less all sites outside of thunderstorms
where strong and variable winds could be possible except KRWL
where gusty winds around 20-25 knots expected.

&&

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

&&

$$

SHORT TERM...MM
LONG TERM...CG
AVIATION...CG