315
FXUS65 KCYS 072337
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
437 PM MST Fri Feb 7 2025

.KEY MESSAGES...

- Strong winds in Wyoming will abruptly change directions from
  SW to W or NW behind a cold front this evening, and then
  gradually weaken through Saturday.

- Intense snow showers along the frontal boundary will lead to
  rapid visibility and temperature drops in Carbon and Albany
  counties this evening. Snow Squall Warnings may be needed.

- Accumulating snow and blowing snow is expected for the
  mountains tonight, including areas of the I-80 corridor above
  7500 ft in elevation.

- Active long term pattern with several shortwaves pushing through
  the region with arctic air returning behind them.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 320 PM MST Fri Feb 7 2025

Current GOES satellite imagery shows increasing cloud cover across
Wyoming as the next potent upper level shortwave surges inland from
the West Coast. Windy conditions continue ahead of this system, with
widespread wind gusts of 50 to 65 MPH over the last several hours.
Strong winds will continue until the front passes through, after
which winds will turn more WNW and remain breezy to windy. A few
gusts to high wind criteria will be possible along the frontal
boundary as well. Several warnings may be able to be cancelled
early, but there is a The surface front appears to be lagging a few
hours behind earlier model projections, but is likely now moving
across central Sweetwater County. Modest instability is present
ahead of the frontal boundary as mesoanalysis shows MUCAPE above 100
J/kg across south central Wyoming along with steep low to mid level
lapse rates exceeding 8C/km. Shower activity developing along and
ahead of the front is indeed displaying a convective nature on
satellite, even picking up a few pulses of lightning. Small, soft
hail was also observed in central Sweetwater County over the last
hour. The environment is thus still ripe for convective rain and
snow showers, but the transition over to snow may occur a little
later than initially thought. The temperature drop may occur with
sundown, which will increase the probability of flash freezing with
any snow shower activity. The main band of strong frontogenesis will
sweep through early this evening, but moist upslope flow will
continue in the higher terrain for several more hours. Forecast snow
accumulations look on track for the mountains through tonight.
Recent HREF component models suggest slightly higher accumulations
(around 1-4") extending into the mid elevations around Arlington/Elk
Mountain and I-80 Summit with gusty winds continuing through the
night. As a result, decided to issue a Winter Weather Advisory for
the snow and blowing snow concerns tonight in these areas, which
will also cover any weaker snow squalls. We will still need to
monitor for the short term higher end squalls that may warrant a
warning and could extend west into Rawlins.

The cold front will sweep through the plains this evening also. The
strong mid-level frontogenesis may still produce some rain and snow
showers, but the window for precipitation will be short. Once the
frontogenesis departs, we will have strong subsidence in the wake of
the upper level shortwave and low-level downslope that will inhibit
precipitation east of I-25. This will also be a second window for
High Winds for the I-80 corridor from the Summit to Cheyenne. 700-mb
winds are slightly marginal around 40 to 50 knots but subsidence
looks strong for several hours of strong winds between about 8PM and
2AM. Saturday looks much colder and breezy across the area, but high
winds are not expected.

Another vort-max will be following behind today`s shortwave and
should arrive tomorrow evening. The mid-level frontal boundary will
be stalled over central Colorado, and the vort-max is expected to
initiate very modest warm air advection overrunning the boundary.
This should re-ignite some light snowfall. While the best
precipitation chances will be to our south in Colorado, light snow
may extend into our far southern zones including the mountains and
the I-80 corridor from the Summit eastward to Sidney. Current
guidance gives a 20 to 40% chance of an inch or more of snow in
these areas Saturday evening. Dry air will move in quickly behind
this vort-max Sunday morning, leading to clearing skies, but still
chilly and breezy conditions for the daytime Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 320 PM MST Fri Feb 7 2025

For the long term period the upper level flow starts
to transition from zonal to a more meridional flow. An amplified
ridge starts to push east from the Gulf of Alaska. This ridge
shifting east creates the opportunity for troughs to drag dry arctic
air down from the Canadian providences and into the Rocky Mountain
region. Monday morning, the 700mb temperatures look to range from
-14C to -20C translating to widespread surface temps in the low
teens to possible single digits to start our day in southeast
Wyoming and the Nebraska Panhandle. As the region progresses through
the day Monday, a weak 700mb will push south leaving a stream of
vorticity to create some precipitation chances for majority of the
area Monday evening through Tuesday morning. Current model guidance
does retain some moisture over the region as the stream of vorticity
moves south. So current estimates looks to generally be under an
inch east of I-25 with the higher totals in the southern counties
collocated with the weak isentropic lift as well. This arctic
airmass will reside over us for a little bit as Tuesday morning
through Thursday morning look to be our coldest temperatures of the
work week. Overnight temperatures have the potential of widespread
single digits with some areas dropping into the negatives. As a
result very cold temperatures remain the primary concern as winds
increase during this time from a strong surface area of high
pressure in the Northern plains dives into South dakota as this
arctic airmass gets a reinforcing shot of colder arctic air from
Canada. Wind chills will have to be monitored for this time period
in case headlines need to be issued.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 423 PM MST Fri Feb 7 2025

Strong westerly flow aloft will continue, while a cold front
moves from north to south across the terminals tonight,
ushering in colder temperatures and a chance of snow.

Wyoming TAFS...For Rawlins, ceilings will range from 1500 to
3500 feet until 10Z, with light snow, blowing snow and fog
reducing visibilities to 1/2 to 4 miles, then scattered clouds
near 10000 feet will prevail after 10Z. Winds will gust to
45 knots until 10Z.

For Laramie and Cheyenne, ceilings will lower to 3000 to
5000 feet after 02Z, with occasional light snow reducing
visibilities to 3 miles from 02Z to 05Z, then scattered clouds
near 10000 feet will prevail after 15Z. Winds will gust to
40 knots until 15Z.

Nebraska TAFS...For Chadron, Alliance and Scottsbluff, ceilings
will range from 3000 to 6000 feet, with occasional rain and snow
reducing visibility to 3 miles and ceilings near 2500 feet until
09Z, then scattered to broken clouds from 6000 to 10000 feet
will prevail. Winds will gust to 30 knots until 09Z.

For Sidney, scattered to broken clouds from 10000 to 15000 feet
will prevail. Winds will gust to 35 knots from 04Z to 13Z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 5 AM MST Saturday for WYZ104.
     High Wind Warning until 7 AM MST Saturday for WYZ106-110.
     High Wind Warning until midnight MST tonight for WYZ107.
     High Wind Warning until 8 PM MST this evening for WYZ109-113.
     Winter Weather Advisory until 5 AM MST Saturday for WYZ110-116.
     Winter Weather Advisory until 7 AM MST Saturday for WYZ112-114.
     High Wind Warning until 8 AM MST Saturday for WYZ116-117.
     High Wind Warning until 7 AM MST Saturday for WYZ118.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...MM
AVIATION...RUBIN