995
FXUS65 KCYS 271743
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1143 AM MDT Tue Oct 27 2026

.KEY MESSAGES...

- Drier and warmer, but windier conditions are expected Tuesday
  into Wednesday with a low potential for High Wind criteria being
  met for the wind-prone areas along the I-80 corridor.

- Quieter weather to end the week, but multiple systems are
  taking shape for the weekend into the start of next week. At
  this time, model agreement is poor so confidence is low.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 202 AM MDT Tue Oct 27 2026

The system that brought SE Wyoming and the Nebraska Panhandle some
beneficial moisture earlier today has since moved off to the north
and east, leaving us in a much calmer pattern over the next few
days. Gauge observations along with MRMS QPE shows totals as high as
0.75" across mainly the southern portion of the Panhandle, with
lighter amounts up to 0.25" across SE Wyoming.

Surface observations at this hour continue to show weak low-level
upslope flow in a rather moist air mass, resulting in areas of dense
fog mainly east of the Laramie Range. Have decided to issue a Dense
Fog Advisory until 9AM MDT for the I-80 corridor including the
summit and points east, in addition to the I-25 corridor where
visibilities less than 1/4 mile have been observed. Low-level
moisture is expected to mix out sometime mid-morning thanks to an
increase in our winds (i.e. mechanical turbulence), and any
lingering fog should dissipate. Tuesday will feature dry conditions
and warmer temperatures relative today ahead of an amplifying wave
located off the Pacific Northwest, placing us under WSW flow aloft.
Expect highs to be around 5-10 degrees above average east of the I-
25, mainly in the low to mid 60s, with slightly cooler 50s to the
west of the Laramie Range. Aside from the notable warming and
clearing relative to the previous couple of days, most will also
notice an uptick in our winds. This will occur as a deeper closed
low phases with a weaker shortwave trough to our north and west,
increasing the height gradient and therefore our mid-level flow.
Westerly 700 mb flow is expected to ramp up to 45-50 knots through
Tuesday morning, with a strong mountain wave signature showing up on
the omega fields, mainly across the Snowy Range and to a lesser
extent the Laramie Range. One limiting factor that will make this
more of a marginal high wind event, rather than a slam dunk, will be
the lack of a mountain top stable layer, as model cross-sections
aren`t showing a tight vertical isentropic gradient (i.e lack of
static stability) at mountain top. In-house random forest guidance
currently has Arlington with a 40% probability of high wind
conditions sometime mid-morning, with Bordeaux at around 20%. Due to
the somewhat marginal high wind setup and relatively low confidence,
decided to keep the High Wind Watch going until 12PM MDT for the
wind-prone areas of the Snowy Range, along with northern portions of
Converse County. Decided to nudge up the wind speeds through Tuesday
morning from the NBM by going with a blend of the NBM 90th
percentile combined with CONS MOS to match the more probable wind
gusts up to 50-55 mph for Arlington and other wind-prone areas along
the I-80 corridor.

Expect a seasonably chilly, but dry night Tuesday into
Wednesday with lows mainly in the 30s and breezy conditions west
of the Laramie Range. With much lighter winds to the east of
the I-25 corridor, along with high-resolution ensemble guidance
having median RH values above 90% in the Panhandle, areas of
fog into Wednesday morning are also possible, especially with
the recent increase in soil moisture from the past system.

The warming trend will continue into Wednesday as upper-level
ridging gradually builds across the eastern half of the country.
Under subsidence, cross-barrier flow (albeit weaker than Tuesday),
and downsloping, can expect another day with above-average
temperatures with highs mainly in the 60s east of the I-25 corridor,
and 50s to the west. Conditions will also be breezy across SE
Wyoming, although most likely below high wind criteria as surface
gradient flow weakens and a rather weak surface low translates to
the north and east over the Dakotas. Overnight Wednesday will be
much like Tuesday night, although perhaps slightly cooler with a
lack of low clouds and light winds. Most locations should hover just
above freezing waking up on Thursday, although the usual cool spots
of Laramie and Alliance dip down to or slightly below the freezing
mark.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 202 AM MDT Tue Oct 27 2026

Mostly quiet weather expected to start the long term forecast as
upper-level flow turns west-southwesterly and weakens for Thursday.
The next upper-level trough will start to become more amplified off
the coast of the Pacific Northwest throughout the day Thursday,
while a shortwave develops off the coast of central California.
Expecting a nice day on Thursday with highs in the upper-50s to
upper-60s across the region with sunny skies turning partly cloudy
into the overnight hours. The aforementioned upper-level shortwave
will move quickly to the northeast Thursday into Friday as it moves
inland with long range models currently suggesting it will impact
the region late Friday evening into the overnight hours. However,
there is some model disagreement on how quick this shortwave ejects
northward. The GFS suggests the shortwave moving through between 06
and 18Z on Saturday, while the ECMWF suggest delayed impact between
18 Saturday and 06Z Sunday. Precipitation chances are anticipated
with the passage of the shortwave, with isolated showers possible
across the Panhandle as early as 18Z Friday, but a delayed shortwave
would delay the increasing precipitation chances across the region.
Clouds will accompany this shortwave, with mostly cloudy skies
expected throughout the day Friday as the shortwave approaches the
region. Friday will be mild with temperatures in the low- to mid-60s
everywhere.

While the longer range models had some significant timing
differences with the upper-level shortwave moving through, the GFS
and ECMWF are in good agreement with the progression of the incoming
upper-level trough. This trough is currently progged to move inland
Saturday evening, strengthening as it does so. The CWA is progged to
be caught between the Sub-Tropical jet across the southern half of
the CONUS and the incoming Polar Jet across the northern half of the
CWA. As a result, a brief period of zonal flow is anticipated early
Sunday morning before upper-level winds turn southwesterly with the
approaching system. Monday onwards, long range models start to
diverge once again with the GFS suggesting the upper-level low
diving southward into northern New Mexico. The ECMWF on the other
hand broadens the low and advects it directly overhead, before
elongating the trough southward Tuesday morning. Both evolutions
would bring widespread precipitation into the region Monday and
Tuesday, but the ECMWF evolution would keep precipitation around
longer, likely leading to higher accumulation values. Another
glaring difference between the GFS and the ECMWF is the 700mb
temperatures associated with this system. The ECMWF is much warmer
than the GFS, keeping 700mb temperatures around -4 to -2C range,
with a brief period of -5C. The GFS, however, suggests a cold system
with a longer duration of -5C temperatures across southern portions
of the region. Both long range models suggest that some snow would
be likely, especially in the overnight hours, with this system, but
the GFS evolution would likely produce more snow, given the longer
duration of colder temperatures. This evolution will continue to be
monitored over the upcoming model runs, to start getting a better
idea of storm evolution and precipitation totals. Despite this,
cooler temperatures are expected to return for much of next
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1140 AM MDT Tue Oct 27 2026

This morning`s round of low clouds and fog is almost cleared
out, and will finish doing so in the next hour. Otherwise, look
for wind gusts between 20 and 30 knots in Wyoming and at CDR
this afternoon (possibly 35 knots at RWL). All except RWL should
ease around sunset, though marginal LLWS is possible at LAR and
CDR overnight.

There is high confidence in another round of low clouds and fog
affecting BFF, AIA, and SNY overnight into Wednesday morning.
Expect this to clear out mid to late morning as winds turn
westerly across the area.

&&

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

&&

$$

SHORT TERM...NB
LONG TERM...AM
AVIATION...MN