440
FXUS65 KCYS 041122
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
522 AM MDT Thu Sep 4 2025

.KEY MESSAGES...

- Strong cold front pushes through the region this afternoon,
  increasing winds.

- Cool temperatures expected Friday and Friday night into
  Saturday, where lows may approach the upper-30s.

- Warming trend returns Saturday onwards.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 128 AM MDT Thu Sep 4 2025

Mostly quiet tonight with only some high clouds drifting across
eastern portions of the region. Clear skies are ongoing out
west as of 07Z this morning. Winds are calm tonight, a stark
difference to what is expected later today in the afternoon
hours. Temperatures have cooled into the 50s area-wide with
light winds leading to a mostly quiet night. No returns on radar
at this time, just mostly clear skies and calm winds.

Conditions are expected to change significantly this afternoon and
evening due to an upper-level low circulating across southern Canada
to the north of the Great Lakes. This low will retrograde slightly
throughout the day, pushing the strong 250mb jet back west with
strong 500mb vorticity advection leading to an additional shortwave
developing through the flow. Down at 700mb, a strong low is present
across southern Canada, vertically stacked throughout the
atmosphere. With minimal steering flow aloft due to the meandering
low, the 700mb will meander as well, with strong winds expected
throughout the associated low-level jet. As this low slowly begins
to lift off to the northeast, a strong cold front will race down
from Canada and drop 700mb temperatures from around 10C down to
about 3C. A strong temperature drop like this favors a very strong
front with strong temperature gradients and pressure gradients along
it. As a result, strong winds are expected across the eastern half
of the CWA this afternoon, with many locations in the Panhandle
gusting into the 40s and 50s this afternoon behind the front. With
dry conditions mostly in place across the region, minimal
precipitation chances are expected, despite the strong cold front
pushing through. A few isolated showers and storms may develop along
the I-80 corridor ahead of the front, but these showers are not
expected to be well organized or long-lived. Therefore, a dry
frontal passage is expected with very strong winds behind it. These
winds will bring a real taste of fall to southeast Wyoming and
western Nebraska as temperatures drop behind the front and the winds
increase towards the typical wintertime winds this region sees every
year. Luckily, high wind criteria winds are not expected with this
front tomorrow. Rather the front serves as some semblance of a
reminder of what is coming not too long from now. The surge of
cooler temperatures will also be felt overnight tonight as lows drop
into the low-40s to near-30s in most locations.

The fall like feel will continue into Saturday with highs in the 60s
for much of Wyoming and 70s for portions of the Panhandle. However,
the real chill will be felt Saturday night into Sunday when
overnight lows drop into the low-40s and even upper-30s in some
locations. Thankfully or, maybe, unfortunately depending on the
desire for fall, temperatures are expected to recover quickly
Saturday through the weekend, with highs on Saturday expected to
return to the 70s and 80s once again.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 232 PM MDT Wed Sep 3 2025

Friday...Cooler and more stable airmass works in in the wake of a
cold front on northwest flow aloft. However, there may be enough
residual moisture and instability to produce isolated afternoon
showers and thunderstorms for the southern Snowy Range and southern
Laramie Valley, otherwise dry. 700 mb temperatures near 5 Celsius
will yield maximum temperatures from the mid 60s to lower 70s.

Saturday...Northwest flow aloft continues with a slow warming trend
as 700 mb temperatures rise to near 7 Celsius. Looks like enough
residual moisture over the southern Snowy Range and southern
Laramie Valley for isolated afternoon showers and thunderstorms.

Sunday...As ridging aloft develops over our counties, return
southeast low level flow develops, advecting low and mid level
moisture across our counties, and producing scattered afternoon and
evening showers and thunderstorms, most numerous west of I-25. The
warming trend continues with 700 mb temperatures near 9 Celsius.

Monday...The warming trend continues with low amplitude ridging
aloft and 700 mb temperatures rising to near 13 Celsius. Adequate
low and mid level moisture for isolated to scattered late day
showers and thunderstorms mainly west of I-25.

Tuesday...As the ridge aloft transitions over the Central Plains
states and our flow aloft turns southwest, temperatures will remain
about the same. Enough low and mid level moisture for isolated to
widely scattered late day showers and thunderstorms, mainly west of
I-25.

Wednesday...Southwest flow aloft strengthens, and with warm
temperatures aloft providing convective inhibition, only isolated
late day showers and thunderstorms will be possible, mainly west of
I-25. High temperatures about the same as on Tuesday.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 515 AM MDT Thu Sep 4 2025

Primary aviation concern this morning will be low ceilings over KAIA
and potentially KSNY, with additional visibility reductions expected
at KAIA. Ceilings at KAIA may briefly become BKN010 or lower, but
confidence in this persisting is low at this time. Included a
TEMPO group for brief improved visibilities and ceilings before
clearing begins. Fog and skies will begin to clear in the next
1 to 2 hours as winds begin to pick up across western Nebraska
and southeast Wyoming. Once skies clear, aviation concerns flip
to strong winds gusting between 30 and 35 kts at most terminals
this afternoon and through the evening hours as a strong cold
front pushes through the region. This front will bring a wind
shift to the north and north- northeast as it passes with winds
continuing to gust behind the front. Timed the front as best as
possible at this time in the TAFs, indicating the wind shift
timing.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...RUBIN
AVIATION...AM/WFO-RIW