468
FXUS65 KCYS 301959 CCA
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
158 PM MDT Wed Sep 30 2026

.KEY MESSAGES...

- A slight chance of rain is possible for the southern Nebraska
  panhandle into Wednesday evening.

- Cooler temperatures continue through Thursday, but warmer and
  drier weather will prevail Friday through early next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 152 PM MDT Wed Sep 30 2026

Tonight...The WSR-88D radar reflectivity from our radar and from
Denver, shows very light bands of rain showers over Morrill and
Cheyenne Counties of the southern Nebraska Panhandle, with this
precipitation so light that much of it is evaporating as it falls
due to the advection of drier air at low levels as seen on the theta-
e advection pattern. Still though, radar reflectivity does show the
northern extent of the rain shield moving slowly northward to
Sterling, Colorado and some of these showers may skirt our Cheyenne
County of the southern Nebraska Panhandle.

Otherwise, the upper trough aloft moves from northeast New Mexico to
the Oklahoma Panhandle by dawn, with cooler air at low levels
advecting into our counties. Quiescent weather anticipated overnight.

Thursday...As the trough aloft opens up and propagates over eastern
Kansas, northwest flow aloft develops over our counties. Atmospheric
moisture looks too scant combined with any lifting mechanisms to
produce any precipitation. 700 mb temperatures near 6 Celsius will
yield maximum temperatures in the lower 60s to lower 70s, with the
coolest readings across the northern Nebraska Panhandle in the
cooler low level airmass behind the dry cold front.

Thursday night/Friday...Northwest flow aloft continues with a
surface trough developing across southeast Wyoming and a
strengthening low level jet forming over the Nebraska Panhandle, with
boundary layer progs suggesting a stratus field and some possible
fog developing across the Nebraska Panhandle, though confidence in
fog development is not sufficient at this time to include it in the
gridded forecasts.

For Friday, the warming trend continues under northwest flow aloft,
with 700 mb temperatures near 10 Celsius yielding maximum
temperatures from the lower 70s to lower 80s. A surface trough will
develop over southeast Wyoming with a decent low level convergence
axis, however, low and mid level moisture will be too scant for any
showers or thunderstorms.

Friday night...Under northwest flow aloft, surface troughing
develops over southeast Wyoming and local mixing effects will
produce a relatively mild night for early October, especially in
Platte County and Wheatland due to downslope katabatic warming.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Issued at 152 PM MDT Wed Sep 30 2026

Global ensemble forecast guidance remains generally unchanged
compared to yesterday regarding the long-term forecast period from
this weekend into next week. High confidence exists for tranquil
weather through much of the long-term period. Large-scale ridging
will dominate the weather pattern over the western CONUS resulting
in generally mild above-average temperatures and limited
precipitation chances over southeast Wyoming and western Nebraska.
This ridging pattern continues to be a result of the highly active
tropical pattern over the eastern Pacific. Numerous EPAC and CPAC
tropical storms will continue to move west and then recurve to the
north in the mid-latitudes of the central Pacific, resulting in
potent synoptic troughing over the Bearing Sea/Gulf of Alaska. This
setup then drives downstream ridging over western North America,
which is apparent once again in today`s ensemble mean guidance. As
mentioned yesterday, these types of stable-synoptic-wave patterns
can often persist for weeks or more, locking in high-confidence
forecasts over much of the west including our region.

Local details remain largely unchanged in the forecast. Above-
average temps are expected each day from Saturday onward. High
confidence exists in temps around 5 degrees above average this
weekend (low to mid-70s east of the mountains) and highs 10 to 15
degrees above average through next week. The one new exception in
the forecast in today`s guidance is a very weak wave in the overall
ridge which may move through on Tuesday. Ensemble guidance has a
very high amount of spatiotemporal dispersion with regard to this
system. Some members do not even show this wave, and others bring it
through strong enough to produce some weak showers over the higher
terrain of southern Wyoming and northern Colorado. We will opt for
the driest solutions for now given recent model performance with
similar systems. Mild temps even during the overnight hours should
continue to hold off the first frosts for any populated areas
outside of the mountains. Afternoon RH values will drop to near or
slightly below 20% throughout the weekend during the afternoon hours
across all of southeast Wyoming and portions of the Nebraska
panhandle. However, generally light surface flow out of the west
less than 20 mph will likely preclude the need for any fire weather
headlines. The synoptic pattern described in both today`s and
yesterdays discussion will continue to result in high forecast
confidence throughout the entire long-term period with limited
societal impacts expected.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1058 AM MDT Wed Sep 30 2026

VFR conditions will prevail at all terminals this afternoon.
Expect high cirrus clouds over CYS and over the southwestern
Nebraska terminals. Ceilings will lower at SNY later this
afternoon but should remain above MVFR thresholds. Forecast
trends have indicated that any shower activity should stay south
and east of SNY leaving all terminals dry through the forecast
period. Dry weather and VFR expected at all terminals on
Thursday.

&&

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

&&

$$

SHORT TERM...RUBIN
LONG TERM...MAC
AVIATION...MAC