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FXUS65 KCYS 182338
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
538 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. 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 FRIDAY/...
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 /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 531 PM MDT Fri Sep 18 2026

A rather tricky forecast for terminals with all flight category
rules on the table. Heavy thunderstorms are spreading east,
currently near KCYS and KLAR. Visibility drops down to 2SM
possible, wind gusts to 45 knots and CIGs reduced to 2 kft
possible. Shower and storm activity becomes more widespread as
it progresses into the NE Panhandle. Post storms a near
saturated surface layer and light winds will be favorable for
widespread fog for the NE Panhandle terminals. The window for
fog development is from around 9z to 16z. Conditions improve in
the mid to late morning, but another round of showers and
thunderstorms in the afternoon hours is expected to bring
similar forecast conditions as this evening.

&&

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

&&

$$

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