402
FXUS65 KCYS 152019
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
219 PM MDT Tue Sep 15 2026

.KEY MESSAGES...

- A wet pattern is expected through the end of the week, with
  almost daily chances for showers and storms.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 216 PM MDT Tue Sep 15 2026

Southwest flow will begin to usher moisture into the area this
afternoon. A weak disturbance aloft will provide lift for showers
and thunderstorms to develop later today. Hi-Res guidance shows
storms forming over the high terrain of Utah and Colorado and moving
northeast into the CWA by this evening. There will be enough
instability to get a few rumbles of thunder, but by the time
precipitation reaches the CWA, it will mostly be stratiform. Showers
are most likely to affect Carbon and Albany Counties later this
evening, but a few showers may be able to cross the Laramie Range
and make it into the Interstate 25 corridor and the Nebraska
panhandle overnight.

A similar day is expected Wednesday, albeit warmer as 700 mb
temperatures rise from southwest flow. Scattered precipitation
chances will continue throughout the day for Carbon and Albany
Counties with vorticity maxes continuing to linger in the area.
Model soundings show decent instability across most of the CWA, so
cannot rule out a few isolated thunderstorms popping up during the
afternoon. Precipitation will become more widespread Wednesday night
as a shortwave moves into Wyoming. This shortwave will bring a
stronger push of monsoon moisture, with mostly stratiform rain
expected overnight.

Rain will continue into the day Thursday, mainly fueled by a surface
low that develops in northeast Colorado and tracks into central
Nebraska throughout the day. Hi-Res guidance shows mostly stratiform
rain, but a few embedded thunderstorms could be possible with model
soundings showing elevated instability. Above average PWATs are
anticipated, so heavy rain will be possible in storms.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 216 PM MDT Tue Sep 15 2026

To start the long term period, Southeastern Wyoming and Western
Nebraska will remain in a southwesterly flow pattern, keeping a
continued influx of monsoonal moisture on the western periphery of a
597 dam ridge centered over the Mid-Mississippi Valley. With PWAT
remaining at or above the 90th percentile for this time of year
(around 0.7"-0.9" inches for SE Wyoming and 0.9"-1.1" for the
Nebraska Panhandle), it will be a matter of how much moisture we can
actually bring to the surface and give us some much needed rainfall.
There is some weak isentropic ascent overnight Thursday into Friday,
mainly over SE Wyoming, however the main shortwave trough looks to
arrive over our area earlier on Thursday when precipitation is
expected to most widespread. Long-range ensemble guidance hints at
non-zero CAPE overnight, but generally under 500 J/Kg, so a few
showers and non-severe thunderstorms can`t be ruled out with the
warm advection regime in place.

On Friday, mid-level flow shifts to more WSW, which will begin to
shut off our source for monsoonal moisture. With some remaining
moisture trapped underneath the ridge (i.e. PWAT still ranging from
the 60th to 70th percentile) combined with another subtle shortwave
trough that skirts across Wyoming and Nebraska Friday evening,
cannot rule out another round of showers and storms on Friday
afternoon and evening. Although LREF guidance has median surface
dewpoints in the mid to upper 50s across the Panhandle, deep-layer
shear is only forecast to be 20-25 knots, which should minimized the
threat of any organized severe weather. At this time, hydrological
impacts/localized flash flooding will be the primary concern, hence
WPC placing our region in another marginal risk for excessive
rainfall on Friday. Coverage is expected to be more scattered and
lower in coverage relative to Thursday, so with less cloud cover we
can also expect highs closer to 80 degrees east of the I-25
corridor, with low to mid 70s to the west.

On Saturday, another weak open wave will translate across SE Wyoming
and W Nebraska. With PWAT still ranging from the the-the
percentile, primarily along the I-80 corridor, can still expect a
few showers and thunderstorms later in the day, but nothing appears
to be widespread at this time. LREF guidance only shows us at a 20-
40% chance of receiving measurable rainfall during this period,
so not exactly enthusiastic that we will see much of any
precipitation that we are desperately in need of. Temperatures
on Saturday will be slightly cooler in the 70s across the
Nebraska Panhandle, and mid to upper 60s for Southeastern
Wyoming.

A shortwave ridge begins to build in to our west on Sunday, placing
us in more of a NW flow pattern. Not only will this decrease our
overall moisture, but with the passage of a weak front sometime
during the day, we can expect a slight cooling trend into early next
week. An open wave will remain situated to our south and west over
California into early next week which will eventually become cut off
from the polar jet to our north, placing us in more zonal flow. This
will translate to a dry pattern with high temperatures sitting right
around climatology (high temperatures in Cheyenne average in the low
to mid-70s next week). It`s too far out to discuss specifics at this
range, but ensemble guidance suggests another longwave ridge
building across the Rocky Mountain West and Northern Great Plains
towards the middle of next week, which would bring a warming trend
to our region.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1131 AM MDT Tue Sep 15 2026

Some low clouds with cloud bases around 4-5 kft are present this
morning under an E/SE upslope flow regime mainly for KSNY, KBFF, and
KCYS. The low-level moisture is expected to mix out shortly after
18Z, with VFR expected to prevail for the remainder of the TAF
period. KLAR and KRWL may have some scattered showers in and around
the terminals later this afternoon into the evening, however
confidence and coverage isn`t high enough to include a TEMPO group,
so opted for VCSH instead. Another round of mid-level clouds is
expected to develop overnight, with cigs well above MVFR criteria.
Winds be primarily remain out of the SE, with peak gusts of 25-35
knots.

&&

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

&&

$$

SHORT TERM...SF
LONG TERM...NB
AVIATION...NB