147
FXUS65 KCYS 081745
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1145 AM MDT Wed Oct 8 2025

.KEY MESSAGES...

- Isolated areas of fog will dissipate Wednesday morning.

- Elevated fire weather conditions are expected over portions of
  southeast Wyoming this afternoon.

- Precipitation chances return for Friday into the weekend.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 400 AM MDT Wed Oct 8 2025

Satellite imagery shows mainly clear skies prevailing over the area
this morning as ridging begins to build back in aloft. Water vapor
channels indicate much drier air moving in aloft from the southwest,
while surface observations show that boundary layer moisture remains
quite good, at least for the Laramie Valley and points eastward.
There is a little bit more of a pressure gradient over the area this
morning compared to 24 hours ago, meaning that winds are generally
not quite as light. With a little more mixing in the boundary layer,
fog coverage is also much more limited than yesterday. Still,
satellite imagery in the fog channels shows a few localized pockets
of dense fog, mainly in southeast Wyoming. This is expected to
expand eastward through sunrise, especially in eastern Laramie
county. Expect any areas of fog to clear up within a few hours of
sunrise.

Temperatures will return to above normal values this afternoon as
much drier air mixes down into the boundary layer. Look for highs in
the upper 60s to 70s with hardly any cloud cover expected (except
possibly around Sidney to Alliance). A typical southwest flow regime
will also set up today with a surface trough more or less along I-
25. This will lead to periods of gusty southwest winds to the west
of the wind shift boundary (which will also be a pseudo-dryline),
and gusty south winds to the east. Fire weather conditions will be
elevated west of the boundary in the southwest flow regime. The
dryline will surge slightly westward overnight, which when combined
with another night of excellent radiative cooling may lead to a bit
more widespread fog production mainly over the Nebraska panhandle,
and seeping into far eastern Wyoming. Patchy fog was added to the
official forecast, most prominently in the North Platte River
Valley.

Thursday will be the warmest day of the week as the ridge axis
amplifies overhead. Expect highs in the 70s to mid 80s, boosted by
westerly downslope flow spreading over the entire area and pushing
the better boundary layer moisture to the east. By the end of the
day, expect to see increasing mid to high level cloud cover as an
impressive moisture surge begins to intrude from the southwest.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 304 AM MDT Wed Oct 8 2025

The flow aloft will turn more southwest as the ridge shifts just to
our east and amplifies heading into Friday. Meanwhile, Hurricane
Priscilla is expected to be moving to the northwest offshore of Baja
California over the next several days. This will seed the southwest
flow with abundant moisture, producing something like a very late
season monsoon surge. Tropical moisture will arrive Friday, and
stick around through Saturday. Precipitable water in the NAEFS mean
is near or above the climatological maximum for this time of year
beginning early Friday and continuing through late Saturday. Look
for deep cloud cover to knock down temperatures at the surface even
while the ridge remains fairly prominent aloft. Despite the nearly
record breaking moisture content, PoPs are not all that high for
this period since there are limited mechanisms to actually get this
moisture to precipitate. Unseasonably warm temperatures aloft will
produce weak lapse rates and little to no convective instability.
Even though the moisture will look like mid-summer, we will likely
need to rely on more typical cool-season forcing mechanisms to get
rainfall out. Orographic lift will likely produce some consistent
shower activity over and adjacent to the higher terrain of southeast
Wyoming beginning early Friday and continuing into Sunday.
Therefore, PoPs are highest in this area. Forcing is trickier
outside of these areas. The first window for some lift will be
Friday afternoon and evening as models are now picking up on a
subtle shortwave trough / vort-max moving across the area. This may
pull shower activity to the east over the High Plains. Another
similar feature is possible on Saturday afternoon and evening,
although this one looks a little weaker. PoPs are generally around
30 to 50% for most of the weekend west of the Laramie range, and 10
to 30% to the east where forcing is more uncertain.

A more powerful northern branch shortwave trough is expected to plow
through the area on Sunday, knocking down temperatures and
suppressing the deep moisture to the south. Models are in fairly
good agreement that the dry slot of this system will be present over
our area, resulting in fairly little precipitation. However, the
official forecast maintains some low-end PoPs to account for a few
showers possibly developing along the frontal boundary. Snow levels
with this cooler system will be low enough to put snow back into the
higher terrain of southeast Wyoming, but QPF is not very impressive
at this time. In addition to a cool down, this system may bring the
first chance of the season for a widespread strong wind event. The
deterministic GFS shows 700-mb winds more than sufficient for high
winds in the wind prone areas, but it is somewhat of an outlier.
Still, about 25% of LREF members show 700-mb winds exceeding 50
knots over the wind prone areas on Sunday morning. Beyond Sunday,
forecast uncertainty increases considerably, but the most likely
synoptic evolution at this time is for the ridge and southwest flow
aloft to amplify once again overhead while the longwave trough
retrogrades and deepens over the West Coast. The result for us will
likely be a continued modestly unsettled weather pattern with
temperatures rebounding back to above average values for this time
of year.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1139 AM MDT Wed Oct 8 2025

Some lingering clouds brining MVFR conditions to KSNY late this
morning, but otherwise expecting VFR conditions and SKC to
prevail this afternoon and evening. Overnight we`re likely to
see some low clouds and possible fog develop in the Nebraska
Panhandle, and most likely sites to see this impact will be KBFF
and KAIA. Winds breezy today with gusts 20-30 knots, strongest
WY terminals.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...MN
AVIATION...CG