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FXUS65 KCYS 091724
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1124 AM MDT Thu Oct 9 2025

.KEY MESSAGES...

- Areas of locally dense fog over the High Plains will dissipate
  by mid morning.

- Precipitation chances return for Friday into the weekend,
  mainly west of I-25.

- After a long summer hiatus, strong winds will return to the
  wind prone areas this weekend.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 315 AM MDT Thu Oct 9 2025

Mainly clear skies are present over the area with a very dry airmass
located over the axis of the upper level ridge moving over our area
this morning. However, surface moisture remains good to excellent
east of a surface trough located near the I-25 corridor. We are
seeing some moisture return surge westward this morning, which when
combined with the subsidence aloft and clear skies, is helping
produce areas of fog and low clouds over the Nebraska panhandle (and
into the lowest elevations of eastern Wyoming). This development is
apparent on GOES fog channels, most prominently within the North
Platte River Valley. There is some uncertainty regarding how dense
the fog will be and how consistent its coverage will be. We will
likely need to put out a Dense Fog Advisory, but will wait an hour
or two to see how widespread the fog becomes. The surface trough
will quickly exit east this morning, turning winds westerly and
clearing out fog by about mid-morning. This will leave us with a
very warm day aided by westerly downslope winds. Expect to see highs
generally in the low to mid 70s west of the Laramie Range, and upper
70s to mid 80s to the east. While about 15 degrees above seasonal
averages, no daily record highs are currently forecast, but some
locations are within a few degrees.

An impressive and unseasonably strong surge of moisture will take
shape over the Four Corners states today, and begin to encroach on
our area late this afternoon and overnight. Southwest flow aloft on
the fringe of a fairly strong ridge over the southern Plains will
tap into abundant moisture seeded by Hurricane Priscilla in the
eastern Tropical Pacific Ocean. Precipitable water is expected to
approach or exceed climatological maximums Friday morning through
Saturday afternoon across most of the area. As this begins to move
in tonight, expect to see mid to high level cloud cover increasing.
Friday and Saturday will be mostly cloudy, so despite mild
temperatures aloft continuing, we will probably lose 5-10F off of
Thursday`s highs for both days. Despite the exceedingly rare
moisture content for this time of year, precipitation forecasts are
rather unremarkable. The issue with this system is that there is
very little forcing for lift to actually extract the moisture as
precipitation. In addition, this will be accompanied by very warm
temperatures aloft (500-mb temperatures near the climatological 99th
percentile), leading to poor lapse rates and little to no convective
instability. The only mechanisms for lift appear to be
orographic (mainly along/west of the Laramie Range), and a few
modest vort- maxes traversing over the area in southwest flow.
There is higher confidence in the former producing shower
activity, which should move into Carbon county late tonight and
continue on and off through early Sunday. Lifting from potential
vort- maxes is more uncertain, with models still in
disagreement whether the lift will be enough to pull shower
activity east of the Laramie Range. If so, the best window will
be Friday evening, but PoPs remain quite low due to uncertainty
in the strength of this lift. While QPF forecasts are minimal
right now, the amount of moisture present will mean that if we
do find some local scale forcing, there could be potential for
decent moderate to heavy rainfall, but the probability of such
an event is too low to add to the official forecast at this
time.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Issued at 315 AM MDT Thu Oct 9 2025

By Saturday evening, a more powerful northern branch trough will
begin to move closer to the area. This looks to move through as an
open wave, with a vorticity maximum traversing across central or
northern Wyoming. This will put our area on the drier and windier
side of the system. Expect a cold front to pass through sometime
Saturday night, pushing the abundant moisture out to the east as a
dry slot in the system comes in overhead. Orographic lift with
strong southwest flow ahead of the front (while we still have
plentiful moisture present) will likely lead to a resurgence of
shower activity over and adjacent to the higher terrain. Cool
air advection will favor dropping snow levels, enough to produce
a few inches of snow over the mountains of southeast Wyoming by
Sunday morning. The more powerful system will also lead to
heightened pressure gradients across the area this weekend.
First, this will be oriented southwest to northeast with
southwest flow aloft and a developing surface cyclone over
northeast Wyoming. Approximately 25% of LREF members have winds
exceeding 50 knots over Rawlins Saturday evening, which would be
marginally supportive of high winds in Carbon County. Then, the
surface front trailing south of the lee cyclone passes through
Sunday morning and leads to a more west to east oriented
pressure gradient and westerly flow aloft. LREF mean 700-mb
winds over the wind prone areas is now around 45 knots, with
about 30 to 40% exceeding 50 knots. The deterministic GFS
depicts 700- mb heights and winds marginally supportive of high
winds, but also with a much more impressive surface pressure
gradient over the gap areas. As a result, confidence is
increasing in at least elevated winds, with probabilities for
high winds in the wind prone areas hanging around 45 to 65%
right now. Temperatures will be knocked down to near or a little
cooler than average for Sunday and Monday behind this system.

By Monday, the lee cyclone will be quickly replaced by a fairly
strong surface high pressure just in the lee of the Rockies in
Montana. This will reverse the pressure gradient and also lead to
increasing south to southeast winds on Monday with cooler
temperatures in place. Aloft, models are in fairly good agreement on
a powerful upper level trough digging into the west coast early next
week which should amplify the downstream ridge over our area.
However, the weather pattern is expected to remain unsettled as the
southwest flow will continue to sweep in moisture and vorticity
associated with the remnants of Hurricane Priscilla. Therefore, low
end PoPs return for Tuesday onward, but overall forecast confidence
is not very high Monday onward due to uncertainties regarding both
the weak disturbances ahead of the main trough, and the timing and
strength of the parent trough`s traverse across the Rockies.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1124 AM MDT Thu Oct 9 2025

Quiet weather is expected throughout the day today with mostly clear
skies. A few clouds may drift into terminals west of the
Laramie Range this afternoon, however these should not pose much
of an impact. Light winds can be expected at most terminals,
however, and occasional gust over 20 MPH will be possible. There
is a slight chance of light showers around KCYS this evening.
This could briefly reduce visibility.

&&

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

&&

$$

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