387
FXUS65 KCYS 071134
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
534 AM MDT Tue Oct 7 2025

.KEY MESSAGES...

- Areas of frost, freezing temperatures, and locally dense fog
  are present Tuesday morning. Additional areas of frost/fog
  are possible Wednesday morning.

- Warmer and drier conditions prevail for Wednesday and
  Thursday, but precipitation chances return for Friday into
  the weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 330 AM MDT Tue Oct 7 2025

The departing trough is apparent on GOES water vapor imagery moving
out of the area this morning. Drier air has pushed in aloft, but
boundary layer moisture remains fairly abundant with near saturation
reported at most stations. A modest surface high pressure is
positioned just to our northeast, but the pressure gradient over our
area is near zero, leading to overall very light winds this morning,
which are expected to continue for much of the day. Areas that have
clear skies are running into localized radiation fog, low clouds,
and frost due to the light winds and high moisture in place. Expect
this to begin to clear up through the morning hours, but some low
cloud cover may linger through much of the day along I-80 from the
summit eastward. Temperatures will be overall near to about 5
degrees below average for this time of year today.

Overnight tonight, expect the surface high pressure to begin to move
off to the east while pressure falls over the inter-mountain west.
This will begin to increase wind speeds again in the form of another
nocturnal low-level jet in the typical spots. Stronger wind speeds
will probably reduce the coverage of fog/frost compared to this
morning, but patchy areas of frost can be expected once again over
the Laramie Valley and points eastward where moisture will remain
plentiful. Drier air will work into the boundary layer in Carbon
County. A ridge will rapidly amplify overhead on Wednesday, boosting
700-mb temperatures to near +10C by Wednesday evening. Expect
daytime highs to climb back to well above average under nearly
cloudless skies. Breezy southwest to south winds may lead to locally
elevated fire weather concerns, but most of the region has seen
wetting rainfall recently.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 330 AM MDT Tue Oct 7 2025

Thursday looks like the warmest day of the week as the amplitude of
the ridge aloft reaches its peak. Expect widespread highs some 10-
15F above average for this time of year in the 70s to mid 80s with
very dry air through most of the profile of the atmosphere. Wind
speeds are expected to come down somewhat for Thursday as the ridge
axis moves overhead. Southwest flow aloft Thursday into Friday will
pick up an immense amount of moisture from the eastern tropical
Pacific ocean, seeded by Hurricane Priscilla. Precipitable water
will rapidly surge from near the climatological 10th percentile
Thursday morning to near or above the climatological maximum by
midday Friday. Dewpoints Friday into early Saturday may get close to
October record highs, especially around the Rawlins area. While
moisture will be exceedingly impressive, part of the contribution to
the high precipitable water values will be near saturation at quite
mild temperatures aloft. As a result, lapse rates are quite
unimpressive and convective instability looks fairly minimal. In
fact, 500-mb temperatures are also close to climatological maximums
during this period. With not much forcing expected too, we may be
looking at quite a bit more cloud cover Friday into Saturday (which
should knock down temperatures a little bit), but with still fairly
limited precipitation chances. The best forcing comes from a few
vort-maxes moving through the area aloft, but timing and track of
this is somewhat uncertain. Currently, the forecast includes PoPs in
the 20 to 50% range during the Friday through Sunday period. This is
highest in Carbon county and over the mountains of southeast Wyoming
where orographic forcing may help extract some precipitation out of
the abundant moisture. We do have a little better forcing on Sunday
as a more powerful northern branch shortwave trough swings across
the area. This features will also knock down temperatures
considerably for Sunday into Monday, at least down to near average
if not several degrees below average.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 530 AM MDT Tue Oct 7 2025

IFR to LIFR conditions have developed at KLAR, KCYS, and KAIA
due to fog and low clouds this morning. The shallow fog at KAIA
should clear out by around 15z, whereas it may take a few more
hours to reach VFR at KLAR and KCYS where the cloud/fog layer is
a little thicker. Additionally, the chance for a temporary drop
into IFR due to fog and/or low clouds has increased for KCDR and
KBFF, but confidence is still fairly low. This was mentioned
with a morning TEMPO group.

The trend should be towards VFR at all terminals for the
afternoon, but some low clouds just above MVFR may linger around
KCYS and the central/southern NE panhandle into the afternoon.
This should finally clear around sundown. Look for increasing
southerly winds overnight at KLAR, KCDR, and KAIA, followed by
another possible round of low clouds or fog, most probable at
KCYS and KSNY towards Wednesday morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Frost Advisory until 9 AM MDT this morning for WYZ108.
     Freeze Warning until 9 AM MDT this morning for WYZ101-102-104-
     110-111.
     Dense Fog Advisory until 8 AM MDT this morning for WYZ116.
NE...Frost Advisory until 9 AM MDT this morning for NEZ002-003-095-
     096.

&&

$$

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