713
FXUS65 KCYS 152302
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
502 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 TUESDAY/...
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 90th to 95th 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 within the 60-70th 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 /00Z TAFS THROUGH 00Z Friday/...
Issued at 459 PM MDT Tue Sep 15 2026

High confidence that VFR will prevail through the TAF period. The
main hazard over the next 24 hours will be scattered, gusty showers
primarily around KLAR and KRWL from around 16Z-20Z, which will have
the capability of brief vis reductions and erratic winds. Added a
PROB30 group at KRWL where confidence and shower coverage is
greatest at this time. There are lower (<30%) chances for showers
and perhaps an isolated thunderstorm at KLAR and KCYS tomorrow
afternoon, however confidence isn`t high enough at this time to
mention in TAFs. This will depend on evolution of mid-level clouds
overnight into tomorrow morning, which will allow for more
destabilization. Otherwise, expect primarily SE winds east of the
Laramie Range, with southwesterly flow prevailing to the west.


&&

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

&&

$$

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