497
FXUS65 KCYS 202113
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
313 PM MDT Sun Sep 20 2026

.KEY MESSAGES...

- Much cooler temperatures expected on Today and Monday behind
  a strong cold front.

- Strong winds will be possible Tuesday night into Wednesday
  morning across the western Nebraska Panhandle with a stout
  low-level jet expected to develop.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 257 PM MDT Sun Sep 20 2026

Today will be the last day of consistently stormy weather across the
area as the low pressure center spins over Casper, WY. Storms are
already ongoing, thanks to the low pressure system pulling moist,
southerly flow into the mid-levels out ahead of it. With cooler
temperatures being observed today, that atmosphere is more stable,
making strong to severe storms less likely later today. Hi-Res
guidance still shows the potential for an isolated strong storm
or two, but model soundings from the GFS show an environment
with only about 500 to 700 J/kg of MUCAPE. This is enough
instability to get thunderstorms, but not strong ones. Showers
and storms will continue into the evening hours for locations in
the Nebraska panhandle as the low pressure system slowly spins
eastward into South Dakota. Once the system makes it east of the
CWA, wrap around moisture could produce a few light showers
overnight in the vicinity of the Pine Ridge from Lusk to
Chadron.

As the trough/low pressure system moves eastward into the center of
the country, shallow ridging will begin to build into the Rockies.
As a result, temperatures on Monday will be a few degrees warmer
compared to Sunday, but still cooler than average for this time of
year. The ridge will also help clear clouds out of the area, lead to
a partly to mostly sunny day across the forecast area. Precipitation
chances are not anticipated, however, a few lingering showers will
still be possible in the Pine Ridge area from the low pressure
system moving out. Overnight, winds will turn southeasterly,
ushering in low-level moisture with fog and low stratus potential in
the Nebraska panhandle.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 257 PM MDT Sun Sep 20 2026

By Tuesday morning, there`s is an area of high
pressure that begins to form over the Great Lakes region as our
former low pressure system enters the Northern plains causing a
traffic jam over the east coast. This becomes our problem as the
ridge builds over us it blocks the weak low pressure system off the
west coast. Multiple shortwaves will be pushing through the
Intermountain west with the first one starting late Tuesday evening
through Wednesday morning for possible light rain showers. With the
later timing off this wave its going to be hard to maintain higher
energy levels needed for severe thunderstorms as the sun angle is
slowly starting to decline. Wednesday afternoon through Thursday
evening looks pretty dry as the Intermountain maintains southwest
flow on the front edge of the ridge advecting in the dry airmass of
the desert southwest. Thursday night into Friday morning another Low
pressure system is progged to push into the Pacific Northwest to
cause some light rain showers to possibly occur Friday. Daily high
temperatures will fluctuate as 700mb temperatures bounce between 6
and 12 degrees C. So on our dry days expect temperatures to range
between the 70`s and low 80`s to 60/70`s on our rainy days.
Overnight temperatures will remain relatively stable with the
overnight lows to remain in the 40`s to with some areas reaching the
low 50`s. This weekend is starting to trend warmer and drier with
the global models wanting to amplify the ridging pattern over us
shifting the potential Low pressure system from Friday further north
into the Canadian Provinces.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1150 AM MDT Sun Sep 20 2026

The upper level low is pretty much over Casper right now. This
low is slowly pushing east but as this thing rotates expect on
and off showers through the Panhandle through 04z for KCDR and
00z for everyone else. However, for the Southeast Wyoming
terminals showers are going to be pretty much done by 19z with a
brief shower possible until 21z just to account for any stray
pop up shower that forms and dies as the low is also rotating.
Also if didnt predict this as well, winds will also be variable
around 10kts with the afternoon gust after this low departs our
area. Some low stratus may also develop again for the Panhandle
at around 12-15z tomorrow morning but should really start to
burnoff by the afternoon.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM...MM
AVIATION...MM