930
FXUS65 KCYS 081730
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1030 AM MST Mon Dec 8 2025

.KEY MESSAGES...

- Snow showers and blowing snow will impact travel in the
  Arlington/Elk Mountain area through Monday morning.

- A long duration wind event is beginning today. While some
  breaks or lulls will occur, high winds will be a concern every
  day through Friday.

- Damaging winds are expected near and in the lee of southeast
  Wyoming mountain ranges Monday evening through Tuesday
  evening. Gusts up to 90 mph are expected.

- Cheyenne, Laramie, Rawlins, Wheatland, and Douglas can expect
  wind gusts up to 75 mph tonight into Tuesday.

- Wind gusts up to 65 mph are expected to spread into High
  Plains during the day Tuesday.

- A backdoor cold front may bring a brief reprieve from the wind
  along with a chance for snow showers Tuesday night into early
  Wednesday before winds pick up again Wednesday.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 400 AM MST Mon Dec 8 2025

Current GOES satellite imagery indicates elevated mid-level
mositure associated with a weak vort-max moving through the
area this morning. This is helping to boost pressure gradients.
Wind gusts of 55 to 65 mph have been ongoing for the last
several hours in the typical wind prone areas of southeast
Wyoming. In addition, moisture embedded in the northwest flow
pattern is forcing some snow shower activity in and near the
mountains of southeast Wyoming. The combination of falling and
blowing snow is leading to reduced visibility and hazardous
travel conditions in the Arlington/Elk Mountain area. Water
vapor imagery shows that drier air is beginning to move into the
area, so expect conditions to improve by around sunrise if not
before. Conditions will remain marginally supportive for wind
gusts to around 60 mph along I-80 all through the day today, so
decided to extend the High Wind Warning for these areas all the
way through the next event (lasting until Friday). Otherwise,
expect a breezy to windy day across the area, but the high wind
threat should remain confined to the wind prone areas (for now).


The main hazard in the short term is the upper tier wind event
expected to begin this evening and last through Tuesday evening. The
wind prone areas may not see a break at all before the next event
Wednesday, but that is discussed more in the Long Term section
below. High wind parameters begin ramping up rapidly after sunset
today as the nose of a powerful jet streak aloft moves overhead. We
will be in the right exit region of this feature, which will help to
support synoptic descent and aid in winds reaching the ground. After
midnight, we will have 700-mb winds exceeding 65 knots over much of
southeast Wyoming. The typical gradients we often look at to gauge
wind potential are about as high as they get. Per the GFS (which is
still running a little hot compared to other models), Craig to
Casper 700-mb height gradients reach 101 meters Tuesday morning.
MSLP gradients from Craig to Bordeaux are sitting between 15 and 20
mb late tonight all the way through the day Tuesday. The MSLP
gradients will be enhanced as a surface trough trailing below a
strong surface cyclone in the northern Plains moves through the High
Plains Tuesday morning. Gradients should peak generally between
sunrise and midday Tuesday. In addition to the impressive wind
parameters, forecast soundings also look favorable for vertically
propagating mountain wave activity. Models are in pretty good
agreement showing a strong inversion setting up between 600 and 700-
mb, which lines up well with mountain top height here. Forecast wind
speeds peak at the inversion level and generally decrease up to
about 500-mb which is a good signal for the potential for mountain
wave breaking and downslope enhancement in the immediate lee of each
of our mountain ranges. All together, the pieces are in place for a
high end wind event between about midnight tonight and Tuesday
evening. The wind prone areas, especially in the lee of the Snowy
and Laramie Ranges (I-25 Bordeaux, I-80 summit/Buford, I-80 Laramie
to Elk Mountain), will likely see wind gusts of 80 to 90 mph during
the peak of this event. While not necessarily likely, it would not
be shocking at this time to see a few gusts in the 95 to 100 mph
range. Southeast Wyoming population centers (including Cheyenne,
Laramie, Rawlins, Douglas, and Wheatland) will probably peak between
65 and 75 mph, but a few brief gusts exceeding 80 mph cannot be
ruled out especially in Cheyenne and Laramie. Once we get some
better mixing in place mid to late Tuesday morning, expect strong
winds to spread all across the High Plains. For far eastern Wyoming
(e.g. Lusk, Torrington, Pine Bluffs) and into western Nebraska,
there is potential for gusts 60 to 65 mph mainly during the day on
Tuesday. Since this threat won`t really begin until Tuesday morning,
decided to let the High Wind Watch continue here to wait for more
confidence, while all other Wyoming zones further west were upgraded
to a High Wind Warning.

Tuesday evening, we will be looking at a surface cold front pushing
through on the front edge of a high pressure system traversing the
eastern edge of the Rockies. This will knock down pressure gradients
considerably as it moves through, and tilt winds more to a northwest
direction instead of due west. This provided enough confidence to
break up the event and end the current set of warnings at midnight
Tuesday night or earlier (with the exception of the I-80 wind prone
areas, which run all the way through). In addition to providing a
brief reprieve from the wind, this front will be accompanied by
potent frontogenesis. This is likely to produce some banded snowfall
Tuesday night into Wednesday morning. Moist upslope northwest flow
will impinge on the mountains once again Tuesday afternoon and
overnight, so periods of moderate to heavy snowfall can be expected
again. Winter headlines may be needed, but the wind threat was the
primary forecast challenge to focus on with this forecast
package.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 400 AM MST Mon Dec 8 2025

The surface high will graze against the Laramie range Tuesday night,
but begin to pull out to the east just as quickly as it arrived. By
late Wednesday morning, forecast models show a surface trough
developing along the I-25 corridor once again, which will help surge
pressure/height gradients once again. As this moves eastward
Wednesday afternoon and evening, winds will overspread the High
Plains once again. Confidence is lower in this event reaching east
of the WY/NE border, but another High Wind Watch was posted from
Wednesday morning into Thursday morning for much of southeast
Wyoming. 700-mb winds climb back up to 55 to 65 knots. The winds
will help temperatures climb again and push the arctic frontal
boundary likely just to the northeast of us (although Chadron may
remain on the cold side of the boundary). Wind parameters during
this second phase of the event are nearly as impressive as the first
phase, but there is a little bit more spread between model systems
at this time.

Thursday and Friday remain a very tricky forecast with the arctic
front right on our doorstep. Overall, most models have trended
towards the warmer, windier scenario, with more ensemble members in
the cluster that keeps the arctic front and associated long-duration
snowfall in northeast Wyoming, southeast Montana, and western South
Dakota. However, this is still uncomfortably close for an arctic
front, as these features can often end up pushing further south and
west than models show. In addition, the surface frontal boundary is
frequently further to the south and west than the mid-level frontal
boundary and associated frontogenesis. Thus, even though the
probability for significant snowfall has decreased, this leaves an
enormous spread amongst ensembles in the forecast temperatures
between Thursday afternoon and Saturday morning, with nearly 20F
between the 25th and 75th percentiles for Cheyenne. There is higher
confidence that areas from Lusk to Chadron or so will be on the cold
side of the boundary. These areas will also have a better chance for
significant snowfall as they will be right on the cusp of the
stalled band of frontogenesis. Considerable uncertainty remains for
this period, so we won`t go too deep into the weeds just yet.

Beyond Friday, models are in fairly good agreement showing the ridge
amplifying and pushing the baroclinic zone further away from the
area. We may finally get a break from the active weather period for
the upcoming weekend with above average temperatures likely.
However, it`s never safe to say that we will get a break from high
winds in southeast Wyoming in December at this lead time.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1030 AM MST Mon Dec 8 2025

In terms of CIGs and VIS, no aviation concerns as VFR conditions
will prevail through this TAF period. Winds will be the primary
threat as they will remain strong and gusty through this TAF period.
Expect westerly gusts up to 40 knots across the Wyoming terminals
and up to 30 knots for the Nebraska terminals. After 07Z Tuesday,
winds really ramp up with gusts in the 50 to 60 knot range across
Wyoming terminals and 30 to 40 knot range for the Nebraska
terminals. Wind shear may be a threat primarily across the Nebraska
panhandle late tonight into tomorrow morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from midnight tonight to 8 PM MST Tuesday
     for WYZ101-104-105-109.
     High Wind Watch from Wednesday morning through Thursday
     morning for WYZ101-107-118.
     High Wind Watch from late tonight through Tuesday evening for
     WYZ102-108-119.
     High Wind Warning from midnight tonight to midnight MST
     Tuesday night for WYZ103-107-114-118.
     High Wind Watch from late Tuesday night through late Wednesday
     night for WYZ104-109.
     High Wind Watch from Wednesday morning through Thursday
     morning for WYZ105-106-113-115-117.
     High Wind Warning until 11 AM MST this morning for WYZ106-117.
     High Wind Warning from 5 PM this afternoon to midnight MST
     Tuesday night for WYZ106-117.
     High Wind Warning until 5 AM MST Friday for WYZ110-116.
     High Wind Warning from 8 PM this evening to midnight MST
     Tuesday night for WYZ113-115.
NE...High Wind Watch from late tonight through Tuesday afternoon
     for NEZ002-003-019>021-054-055-095-096.

&&

$$

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