479
FXUS65 KCYS 211749
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1049 AM MST Fri Feb 21 2025

.KEY MESSAGES...

- Steady warming trend through mid next week with highs
  returning to the 50s and even 60s

- Potential for a long duration high wind event this weekend and
  through early next week, especially for the wind prone areas

- Warmer, drier, and windier for Monday through mid-week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 250 AM MST Fri Feb 21 2025

Relatively quiet weather tonight as a weakening Pacific upper
level trough moves eastward across the eastern Colorado
plains...well south of the Colorado/Wyoming border. IR Satellite
loop shows cloudy skies to the north over most of southeast
Wyoming and portions of western Nebraska, but little if any
precipitation has been observed. Will likely let the Winter
Weather Advisory for the Sierra Madre Range to expire on time
with snow accumulations mostly under 3 inches across the higher
mountains. The upper level trough will continue to weaken this
morning as it moves southeast into Kansas. Early morning
temperatures are not nearly as cold as they`ve been recently
with the cold spots mostly over western Nebraska with readings
around 0 degrees. It gradually gets warmer as you head into
Wyoming with lows likely in the teens to low 20s by sunrise
Friday.

The much-anticipated warming trend will begin today and
continue through this weekend as a broad upper level ridge axis
expands northeast into the Front Range. Today will be mostly on
the cool side due to the lingering snow pack, but seasonable
for this time of the year, with highs in the mid 30s to low 40s
across southeast Wyoming eastward into western Nebraska this
afternoon. 700mb temperatures will climb above 0c for this
weekend with high temperatures rebounding into the 40s to low
50s after a cold start Saturday morning. Even though a weak
shortwave disturbance aloft will move southeast across the area,
temperatures will continue to climb on Sunday with highs likely
in the 50s to low 60s possible. Did not increase temperatures
quite as high as guidance due to the snowpack, but if most of
the snow melts by Sunday, mid 60s aren`t out of the question
Sunday afternoon.

Attention will then shift to increasing winds across southeast
Wyoming this weekend with all in-house wind models showing an
impressive wind event for at least the wind prone areas. Timing
of this event is very tricky, at least with the forecast
onset/start time. Previous models runs were suggesting late
Friday night and early Saturday, but most guidance is starting
to trend away from High Wind criteria that early. Some in-house
guidance still shows locally strong winds beginning late Friday
night for the wind prone areas, but marginal surface gradients
from high res guidance and the NAM/NAMnest, and weak low level
subsidence suggest windy conditions but not High Wind criteria.
The weak upper level disturbance sliding southeast into the
forecast area on Saturday may have something to do with the poor
low level pressure gradients and generally poor gap-wind
environment Friday night through Saturday night. However, once
this disturbance moves southeast of the area late Saturday
night, all models show rapidly increasing low to midlevel
pressure gradients and 700mb winds increasing over 50 knots.
Issued a High Wind Watch for Bordeaux (I-25) and Arlington/ELk
Mountain (I-80) starting Saturday evening. Added the I-80 Summit
and Foothills to the Watch starting 500 AM Sunday morning. This
wind event will likely last multiple days and may include the
sub- wind prone areas of southeast Wyoming. Please see the Long
Term discussion below for additional details.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Issued at 205 AM MST Fri Feb 21 2025

The windy period for southeast Wyoming continues into the middle of
the week as High Wind Watches remain in effect until 11pm Tuesday
night. Not much has changed forecast wise in the long term portion,
with only slight changes to the strength of the systems pushing
through and giving the region high winds. With primarily
northwesterly flow aloft, multiple disturbances will be able to
propagate through the flow, leading to the continued threat for high
winds. The first of two Alberta Clippers traverses into the Great
Lakes region Monday morning and is more diffuse than previous
forecast runs. Despite that, this system will still act to increase
height gradients on the 700mb level, leading to a 60-65kt jet
overhead throughout Monday morning. Craig to Casper 850mb gradients
increase into the upper-70s and mid-80s during this time frame, with
700mb gradients not too far off in the low- to mid-60s. Surface
pressure gradients will also strengthen in response to the low
pressure system moving into the northern CONUS. The second of the
two Alberta Clippers develops throughout the morning into the
afternoon hours on Monday. This system will be much more potent than
the first, leading to a 65-70kt 700mb jet overhead at the peak
strength of the system Monday evening. Craig to Casper gradients
increase into the 80s to near-100m during this time before slowly
tapering off. In-house random forest guidance continues to suggest
around a  80 to 90% probability for high winds at both Arlington and
Bordeaux, with a still impressive 40% probability for high winds
over Cheyenne at the 18Z Monday to 00Z Tuesday timeframe when the
system is at its peak. Strong downward omega fields will also be
present from Sunday evening through early Tuesday morning, further
favoring continued high winds across much of southeast Wyoming. At
the peak of the wins between 18Z Monday and 00Z Tuesday, high winds
spreading towards the Nebraska border cannot be ruled out at this
time, but more decisions will be made about this event as it gets
closer. On benefit of the strong winds will be the much warmer than
average temperatures expected Monday and Tuesday, with highs in the
50s and 60s east of the Laramie Range where the best downsloping
will be occurring. Highs in the 40s and 50s expected west of the
Laramie Range.

Winds will finally taper off late Tuesday night into the early
morning hours of Wednesday, ending the roughly 75hr period of high
winds across southeast Wyoming. An upper-level trough will have just
pushed through the region by Wednesday morning, with a building
ridge just off to the west of the West Coast. Northerly to
northwesterly flow will remain as this ridge slowly pushes inland
and strengthens throughout the day Wednesday into Thursday. This
ridge will favor warm temperatures and dry conditions through the
middle of the week, with minimal chances of precipitation expected
prior to Wednesday. After a quick passage of a cold front Tuesday
night into Wednesday, Wednesday`s temperatures will likely be the
coldest of the week in the 40s and 50s area-wide. Temperatures begin
to warm up again Thursday as the upper-level ridge pushes overhead.
Expect highs to return to the 50s to near-60s Thursday and Friday,
with minimal precipitation chances and relatively calm winds.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1029 AM MST Fri Feb 21 2025

The cloud deck is starting to clear out across the region, but
expect ceilings around 2.5-5k feet to linger for RWL/LAR/CYS for
another couple of hours before clearing out. After that, either
clear skies or high scattered clouds expected, along with winds
generally on the light side outside of RWL where gusts 20-30
knots are possible.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Saturday evening through Tuesday evening
     for WYZ106-110.
     High Wind Watch from late Saturday night through Tuesday
     evening for WYZ116-117.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...AM
AVIATION...CG