188
FXUS65 KCYS 041749
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1149 AM MDT Sat Oct 4 2025

.KEY MESSAGES...

- There is a Marginal Risk (Level 1 of 5) for severe weather
  across all of southeast Wyoming and western Nebraska today.

- Strong winds possible at Arlington, Bordeaux, and the I-80
  Summit this afternoon and evening behind the cold front. Gusty
  winds expected everywhere behind the front.

- Precipitation chances continue into Sunday with temperatures
  10 to 20 degrees cooler than Saturday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 250 AM MDT Sat Oct 4 2025

Much more moisture around the region tonight as low- and mid-level
clouds move across much of the CWA with embedded showers and event a
thunderstorm over near Rawlins as of 08Z this morning. GOES 19 Mid-
level Water Vapor shows the strong trough, currently over Nevada and
western Utah, with ample moisture being funneled into the region. A
very weak low-level jet was keeping elevated winds ongoing at
Chadron, but these surface winds have since calmed down to around 6
mph. Temperatures remain mild overnight with temperatures currently
in the low-60s to mid-60s, with Chadron sitting around 68F due to
light downslope ongoing in that region. As is the case for much of
today, the region currently sits in the warm sector of the system
moving into the region, further showing why temperatures remain
fairly mild tonight.

Later this morning, the upper-level system will push eastward
towards the region, with a strong southerly to southwesterly jet
around 100kts. For most of the day, the region will be in the warm
sector of the system, with 700mb temperatures remaining in the 8 to
10C range until mid-afternoon. As this trough pushes closer to the
region, synoptically-driven ascent will develop across the western
zones and slowly spread north and eastward as the trough continues
its eastward propagation. At this time, some showers have been
pushing across the region, west of the Laramie Range. Showers will
become more numerous to widespread as the upper-level trough
continues its eastward push and the strong, synoptic ascent impacts
more of the region. Strong 500mb vorticity advection will deepen a
portion of the broader trough into a potent short wave this
afternoon, which will dig across the region southwest to northeast.
Coincident with the strengthening of the shortwave, a strong surface
cyclone will develop across northern Colorado and quickly migrate
northeastward towards central Nebraska and central South Dakota,
placing the CWA in the northern to northeastern sector of the system
throughout the day. In the middle of winter, this would be a decent
setup for snow across the region, however, the 700mb are expected to
remain warm through the evening, with the cold front not arriving
until about 20 to 21Z. Temperatures quickly cool from around 8C down
to 2C as the cold front drags across the region. 700mb temperatures
will continue to cool overnight into Sunday on the backside of the
departing shortwave. Therefore, precipitation will start to become
more widespread this morning and is expected to remain rain for most
areas. Precipitation will continue through the day, but will become
less widespread later in the evening. There is some marginal CAPE
present across the region, so some storms may become stronger with
the threat of gusty winds and small hail. As a result, there is a
Marginal Risk (Level 1 of 5) for severe weather across the entire
region. However, areas above 9000ft elevation will likely see rain
switching to snow. The Snowies and Sierras look to pick up 1 to 4
inches of snow with this system.

As is fairly typical with a system like this, strong winds are
expected in the wind-prone regions of southeast Wyoming.
Arlington/Elk Mountain, Bordeaux, and the I-80 Summit may see winds
gusting to 55mph or higher this evening behind the cold front. A
strong temperatures gradients will keep winds very breezy behind the
front, with the passing 700mb trough increasing winds at Bordeaux
and the I-80 Summit later this evening. The base of the 700mb trough
will move across the CWA with an associated 50kt jet early Sunday
morning around 09Z. This will keep locations very windy through the
overnight hours. Bordeaux and the I-80 Summit may see a brief period
of 60mph wind gusts, however, the duration of these gusts looks to
be fairly short, so chose not to issue a High Wind Warning as high
wind criteria will likely only be met for an hour or two this
evening/overnight. In-house guidance is pinging about at 60% chance
for high winds at Arlington, but likely only over a 2 to 3 hour
period. Additionally, other variables associated with strong winds
at Arlington remain a bit lower than is preferred for High Winds.
Therefore, did not issue a High Wind Warning for the Arlington zone
either.

For Sunday, the main upper-level trough will continue to slowly
evolve and become more positively tilted by 09Z Monday with an axis
from northwestern North Dakota southwestward to south central
California. 700mb winds will slowly decrease through the morning
hours, resulting in decreasing winds across the wind-prone region.
Temperatures will be much cooler on Sunday, around 10 to 20 degrees
colder than Saturday. Precipitation chances will continue throughout
the day Sunday as additional synoptic lift from the primary trough
impacts the region. The lift this time around will be weaker and
broader than with the potent shortwave on Saturday. As a result,
precipitation coverage will decrease, but most areas will still see
some light rain throughout the day. As cold air at 700mb settles
over the area, many higher elevation locations will continue to see
snow chances, with some adjacent zones seeing a few flakes mixed in
with the rain. Mainly Laramie looks to have the best chance of
seeing some flurries. The I-80 Summit may see snowfall as well,
though likely not enough to amount to anything significant.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 300 PM MDT Fri Oct 3 2025

Sunday starts an active beginning of the week as
upper level trough pushes through the Intermountain West. This
trough carries some colder air behind it dropping 700mb heights into
the -2 to -5 range. This will keep in the 50/60`s for Sunday and
Monday. This trough also brings some precipitation chances Sunday
afternoon through Monday morning. The Southeast corner of Wyoming
and the Nebraska Panhandle will remain in the "Warm Sector" of this
trough likely keeping the precipitation rain below 8,500 ft meaning
a chance for snow for our mountain tops. However, during the
overnight period Sunday night into Monday morning temperatures will
drop into the 30`s and low 40`s likely creating some frost in the
early morning Monday and possibly Tuesday morning as well. Due to
the passage of this trough, the pressure gradient will tighten
across the forecast area creating gusty conditions Sunday into
Monday afternoon as well. Starting Tuesday, another ridge slowly
starts to build over the Intermountain West. There is a weak
shortwave that passes through the Intermountain West, but the
associated precipitation chances looks to be isolated to the
mountains Tuesday afternoon and evening. However, temperatures do
start to gradually warm up returning to the 60`s and 70`s by
Wednesday afternoon.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1147 AM MDT Sat Oct 4 2025

Active weather expected at all terminals today as a large scale
storm system moves across the forecast area. A strong cold front
will push across the area, bringing widespread precipitation.
Showers and thunderstorms are expected, with some storms having the
capability of producing strong wind gusts. Moderate to heavy rain
can also be expected, which will likely cause visibility drops below
VFR criteria at times. Coverage of precipitation will lessen later
this evening, however a few lingering scattered showers and
storms will be possible. Behind the cold front, low CIGs will
start to build in, mainly affecting areas west of the Laramie
Range overnight. More precipitation and low stratus will move in
on Sunday.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...MM
AVIATION...SF