198
FXUS65 KCYS 111144
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
544 AM MDT Sat Oct 11 2025

.KEY MESSAGES...

- Another round of scattered showers and isolated thunderstorms
  is expected today. A few strong storms are possible, mainly in
  Carbon County.

- Light snow accumulations are on track for the mountains of
  southeast Wyoming Sunday morning.

- Widespread strong winds are expected late tonight through
  Sunday afternoon. Fire weather conditions will be elevated
  over the High Plains.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 430 AM MDT Sat Oct 11 2025

Abundant moisture continues to stream in over the area from the
southwest this morning. Tropical Storm Priscilla has dissipated in
the eastern Pacific, but its remnant moisture remains over the Four
Corners states, and is flowing up into southern Wyoming and western
Nebraska as well. Precipitable water is hovering near climatological
maximums, with nearly fully saturated soundings and surface
dewpoints near record highs for October. This weather pattern is
much more reminiscent of a powerful August monsoon surge rather than
mid-October! At this hour, the area is somewhat in between
shortwaves. The first that brought Friday`s light shower activity
through the area is now moving east across South Dakota. The next
wave is apparent on GOES satellite imagery as an area of colder
cloud tops encompassing much of the state of Utah currently. As this
moves northeast into Wyoming, expect to see showers fill in again in
Carbon county this morning, reaching the I-25 corridor around noon.
Model guidance has trended slightly stronger with this feature,
leading to a little bit more organized forcing for ascent than
indicated 24 hours ago. Global models have picked up on some subtle
overrunning lift just ahead of the shortwave trough axis aloft. This
is likely why Hi-res models have also trended towards much greater
coverage of showers today. We also expect to have slightly more
instability present today compared to yesterday, so a few more
isolated thunderstorms can be expected through the day. Showers
should clear out once the trough axis passes overhead, which looks
to be mid-afternoon around I-25 and around sunset for the Nebraska
panhandle. Probabilities for wetting rainfall have increased a
little bit, but QPF is still modest. Areas along and west of the
Laramie range have generally a 50+% chance for a tenth of an inch of
rainfall today, while these probabilities remain around 10 to 20% to
the east per the HREF system. Still, the High Plains can expect to
see some light showers once again, so at least a slight chance was
maintained in the official forecast through the early evening.

Look for a brief break in the active weather this evening before
another much more powerful storm system swings into the area
tonight. Widely scattered showers and thunderstorms are expected to
move back into Carbon county around sunset as forcing and moisture
increase again ahead of the northern branch upper level low
approaching. Moist southwest flow will favor steady-ish
precipitation in the mountains with orographic lift and scattered
activity in the adjacent zones. This will also bring very rapid cold
air advection, sending snow levels plummeting this evening. Expect
rain to switch over to snow quickly in the mountains. Much of Carbon
and Albany county have the potential to see some flakes flying, but
it will be a race between the plummeting snow levels and the dry air
rapidly moving in behind the cold front shutting off the
precipitation potential in general. Therefore, a rain-snow mix is
mentioned for much of these areas, but PoPs are quite low. The
strong orographic lift will be brief, but should be enough for a few
inches of snow to accumulate in the higher terrain. Currently, this
is most likely to be sub-advisory.

This strong system is expected to track well to our north, putting
most of the forecast area in the dry, subsident zone on Sunday. The
primary impact for most of our area will be widespread strong winds.
The surface cold front is expected to push into Carbon county around
midnight tonight, and then race eastward, reaching Sidney by around
6AM. Very rapid pressure rises are expected behind the front, which
will put a strong surface pressure gradient over the gap areas in
the several hours following the frontal passage. In addition, flow
aloft will be quite strong under the base of the trough axis Sunday
morning. LREF mean 700-mb winds now exceed 50 knots over the wind
prone areas of southeast Wyoming, and are around 40 to 45 knots for
the rest of the area. In-house guidance has landed around 50 to 60%
probabilities for winds exceeding 50 knots in the typical locations,
which provides enough confidence to issue a High Wind Watch. The
highest confidence is for the wind prone areas along I-80, while
confidence is lower along I-25. A few mesoscale models are showing a
surface trough developing very close to the crest of the Laramie
Range concurrent with a signal for ascent on the upward flank of a
standing mountain wave. If this occurs, the strong winds might
struggle to reach all the way east to I-25. These areas were still
included in the watch though, as there is potential to temporarily
reach the highway with the aid of a breaking mountain wave, and/or
mixing later in the day (although wind speeds aloft peak in the
morning). While not included in this watch, Converse county and
northern Carbon county will also need to be considered with the next
forecast package. Gusts of 50 knots or greater should be mainly
confined to the wind prone areas, but it will be a windy day by any
definition for essentially the entire area on Sunday. We may need to
watch a few localized areas for gusts approaching 50 knots,
particularly the Wildcat Hills area in the southern Nebraska
panhandle, but confidence was too low to include in the watch at
this time. Still, most of the area can expect consistent gusts of 40
to 55 mph through Sunday, waning quickly after sunset.

Winds should shut off quickly Sunday evening as a surface high
pressure system settles in overhead. With clear skies, light winds,
and a drier airmass in place, we should see pretty effective
radiative cooling. Most of the area will have a chance at a season-
ending freeze for Monday morning, but it may be more confined to
local low spots rather than clearly encompassing the entire
area.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 430 AM MDT Sat Oct 11 2025

A fairly unsettled weather pattern is expected to carry through much
of the week ahead. The storm system will quickly move off to the
east on Monday, while a very powerful closed low dives into the
California coast. This will help to re-amplify the upper level ridge
over Texas and nudge temperatures upward through mid-week.
Considerable moisture is expected to remain over the Four corners
states, which may then get drawn northward into our area once again
by the end of the day on Monday. A vort-max getting pulled out of
the southwest will keep some showers around the area Monday evening
into Tuesday in a continuation of this pseudo-monsoonal pattern well
outside of its typical season. Most of this activity looks to be
fairly minimal through Wednesday, but low-end PoPs are retained in
the forecast for this unsettled weather. A more significant system
is possible sometime between Wednesday evening and Friday
morning time period when the aforementioned closed low ejects
across the northern Rockies. Models differ significantly in the
exact track and timing of this system, so we won`t get too deep
into the weeds right now. The main take-away is that there is
potential for widespread rain showers, along with a slim chance
for snow especially west of the Laramie range.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 537 AM MDT Sat Oct 11 2025

There are several aviation hazards over the next 36 hours or so.
First, low CIGs are present near High Plains terminals (except
KCDR) this morning. This cloud deck is right on the edge of
several terminals, so temporary fluctuations in flight category
are likely. This should improve by about 16z.

Next, an area of showers is expected to move in from the
southwest today. Rain will fill in first at KRWL mid-morning,
and reach the NE panhandle by mid-afternoon. Expect about 3-6
hours of light rain, with brief moderate rainfall possible
especially at KLAR. While this should still be mostly VFR, most
terminals can expect a brief drop to MVFR VIS and/or CIG with
today`s rain showers. Thunder can`t be ruled out, but the
probability was too low to include in the TAF at this time. If
an isolated thunderstorm strays near a terminal, look for brief
moderate to heavy rainfall possibly to IFR and gusty/erratic
winds. Cloud cover will clear out behind this batch of showers.
There is about a 30% chance for fog and/or low clouds to develop
Sunday morning near KBFF, KAIA, and KSNY.

Lastly, a strong cold front will sweep through overnight
tonight. This will bring another round of rain possibly mixing
with snow to KRWL after midnight. Other terminals are unlikely
to see precipitation from this round, but can expect a wind
shift to the west which will quickly become gusty early Sunday
morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from late tonight through Sunday afternoon for
     WYZ106-116.
     High Wind Watch from Sunday morning through Sunday afternoon
     for WYZ107-117.
     High Wind Watch from late tonight through Sunday afternoon for
     WYZ110.
NE...None.

&&

$$

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