852
FXUS65 KCYS 211112
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
512 AM MDT Mon Sep 21 2026

.KEY MESSAGES...

- Cool and seasonable temperatures will continue through mid-
  week, with a warming trend expected for the second half of the
  week into the weekend.

- Daily precipitation chances will start to decrease Tuesday and
  Wednesday, with limited to no precipitation chances to end the
  week.

- Breezy conditions will be possible across much of the region
  Tuesday and Wednesday, especially across the western Nebraska
  Panhandle.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 231 AM MDT Mon Sep 21 2026

Upper-level troughing will finally move out of the region today as a
weak ridge develops across the Rocky Mountains on the backside of
the trough. The ridge will remain modestly strong throughout the day
Monday as another upper-level trough attempts to develop over
Nevada. This setup results in a fetch of southwesterly flow all the
way to the Pacific Ocean, acting to continue funneling in moisture
to the region. With fairly turbulent flow behind the departing
trough, a few 500mb vorticity maxima push across the CWA later this
morning into the afternoon hours. As a result, weak synoptic forcing
for ascent will be present, despite the broad sinking motion
expected beneath a ridge. Stronger 500mb vorticity maxima will
remain off to the west, associated with the developing trough. 700mb
flow will be weak this morning and afternoon as a weak ridge
develops overhead this morning. This ridge will strengthen
throughout the afternoon hours today, resulting in increasing height
gradients across the region and a weak 25kt low-level jet east of
the Laramie Range. Warm air advection will be present at 700mb this
afternoon, increasing 700mb temperatures from 1 to 4C this morning
to 5 to 9C by the evening hours. With the stream of upper-level
moisture advecting into the region today and broad, weak synoptic
forcing, partly to mostly cloudy skies will prevent significant
warming this afternoon with increasing 700mb temperatures. Surface
high temperatures are currently forecast to be in the low-60s to low-
70s once again. Isolated showers will be possible in the northern
Panhandle this afternoon, but should diminish by 9PM this evening.

Upper-level ridging will continue across the central CONUS on
Tuesday, with the upper-level trough over Nevada starting to eject
northeastward throughout the day. As the trough moves closer to the
ridge, 250mb height gradients will increase, leading to a nearly
90kt jet from northeastern Utah through northeastern Wyoming.
Additionally, this placement will once again put the CWA in a
favorable region for dynamic lift downstream of the trough axis, so
synoptic forcing for ascent will be present and stronger on Tuesday.
500mb vorticity maxima will eject out ahead of the incoming trough,
but currently look to be more concentrated across central Wyoming,
rather than southeast Wyoming. Combining this with continued 700mb
warm air advection Tuesday, favorable synoptic forcing will be
present across much of the CWA. Isolated to scattered showers will
be possible again Tuesday afternoon, but will likely remain confined
to areas west of the Laramie Range where additional synoptic forcing
is present. A stout surface high pressure system over eastern Canada
will continue to strengthen on Tuesday, influencing surface winds as
far west as the Wyoming/Nebraska border. A strong surface pressure
gradients is expected across western Nebraska throughout the day and
evening hours Tuesday, resulting in fairly strong surface flow. The
GFS suggests a 40kt 800mb low-level jet over the Panhandle Tuesday
afternoon through the early morning hours Wednesday. Sustained
surface winds are expected to be between about 20 and 25mph Tuesday
afternoon and evening with gusts well over 40mph in many locations.
While this is not high wind criteria winds, it will still be a very
breezy day and night across western Nebraska.

The ridge will continue to strengthen on Wednesday with stout,
southwesterly to southerly flow expected at 250mb. The shortwave
trough will quickly eject off the the northeast as the ridge
prevents it from moving across much of the CONUS. However, the
turbulent flow from this will result in 500mb vorticity maxima
pushing across the region again Wednesday though the strongest
vorticity band looks to remain just to the southeast of the CWA. A
diffuse 700mb shortwave will move from eastern Montana northeastward
away from the CWA and into Canada, but not before kicking up some
breezier winds across the western portion of the CWA Wednesday
afternoon. Once again, high winds are not anticipated with this
shortwave, but breezy conditions will be present for the afternoon
hours. Limited precipitation chances are anticipated for Wednesday
as much of the better forcing for ascent remains away from the CWA.
Cloud coverage will continue to prevent afternoon high temperatures
from reaching very warm conditions, with the current forecast for
high temperatures on Wednesday in the upper-60s to upper-70s across
portions of western Nebraska. If any location were to get
precipitation on Wednesday, it would likely be across the Panhandle
where warmer temperatures will be present. However, significant
rainfall is not expected.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Issued at 231 AM MDT Mon Sep 21 2026

Thursday onwards the CWA looked to remain largely in between the
upper-level ridge to the south and east and an incoming upper-level
trough to the west and north. Southwesterly flow aloft is expected
to continue, with the Pacific Ocean fetch once again setting up
across the western CONUS. A few lobes and bands of 500mb vorticity
will move through the region throughout the end of the week, but
precipitation chances remain quite low through the weekend. 700mb
flow will remain variable and fairly weak Thursday through the
weekend, leading to a much quieter end of the week as compared to
the start of the week. 700mb temperatures remain between about 8 and
10C Thursday through the weekend, favoring seasonable, if not
slightly above average, temperatures. Daily high temperatures will
be in the 60s and 70s for most of the area, with 80s possible in the
North Platte River Valley and across much of the Nebraska Panhandle.
Saturday looks to be the warmest day, as westerly 700mb flow
promotes some weak downsloping along and east of the Laramie Range
and downslope warming increasing temperatures to the east. With the
warmer temperatures, afternoon minimum humidity values will start to
drop back into the 25 to 30 percent range to end the weak, leading
to slightly elevated fire concerns Thursday onwards. Red Flag
Warnings are not anticipated at this time, as the southwesterly
fetch of moisture should keep the surface moist enough to prevent
critical humidity values from developing. Additionally, overnight
humidity recoveries will be above about 70 to 80% most night through
the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 509 AM MDT Mon Sep 21 2026

Low clouds and patchy fog have moved in across the western
Nebraska Panhandle, impacting KBFF, KCDR, and KAIA as of 11Z
this morning. IFR conditions are expected to develop at KCDR and
KAIA this morning with low clouds around 600ft. The Panhandle
will not clear out much this morning, but ceilings will increase
to MVFR and VFR conditions by 18Z. The Wyoming terminals will
see mostly clear skies with patchy fog possible near KLAR for
the next hour. Skies remain mostly clear this afternoon for the
Wyoming terminals.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...AM
AVIATION...AM