621
FXUS65 KCYS 050510
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1010 PM MST Tue Feb 4 2025

.KEY MESSAGES...

- A stationary surface cold front against the Laramie Range will
  bring chilly temperatures to areas east of the Interstate 25
  corridor today. Mild temperatures expected west of the Laramie
  Range.

- High Wind Watches and Warnings issued for the southeast
  Wyoming wind prones and adjacent areas for Wednesday.

- Mild to end the week, with snowfall chances and very cold
  temperatures returning for the weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 140 PM MST Tue Feb 4 2025

Latest upper air analysis depicts southwesterly flow continuing to
build across the west CONUS, as the broad upper level ridge begins
to set up across the High Plains. Similar to yesterday, temperatures
have been tricky throughout the day, with the cold front that
dropped south yesterday remains stalled across the Laramie Range,
creating another day with a sharp temperature gradient and very
dramatic temperature differences as areas west of the Laramie Range
are in the low to upper 50s and into west Nebraska have reported
temperatures below freezing. Nevertheless, some relief is in sight,
with some mixing of the colder airmass locked across Laramie county
as temperatures continue to rise a good 10F within the last hour and
some signs that mixing will continue eastward. Unfortunately, this
might not have as much influence into western Nebraska as it did for
the I-25 corridor with overnight lows in the teens, indicating only
a small amount of recovery before sunset.

Outside of temperatures, main concern in the near term forecast
remains centered on the next High Wind event, progged for early
tomorrow morning across southeast Wyoming. Models have been
consistent with a developing surface low across the area and
tightening MSLP gradients . Higher confidence with the newest high
wind threat today, with Craig to Casper gradients continuing to rise
with each new model run, ultimately maxing at 65/60 meters at
850mb/700mb. Combined with local in-house model guidance having
areas long the I-80 corridor probabilities of reaching strong winds
at 50% to 60% and the NBM v4.2 Probability of Exceeding 41kts have
begun picking up on greater than 90% probabilities for all areas
north and west of the Laramie Range. With increased model support,
went ahead and upgraded all zones west of the I-25 corridor, and
further northward including Converse county, into High Wind
Warnings. Only zones left into a watch include central Laramie
county, east Platte county, and Bordeaux, where lower confidence
remains. While the GFS has been the best advocate for high winds
across these zones, the NAM has been the most favored during this
high wind season having relatively better detection for the stronger
flow and has indicated that the stronger gradients will remain to
the west. In addition, both in-house model guidance and the NBM v4.2
Probability of Exceeding 41kts align better with the NAM having much
lower probabilities for strong winds in the aforementioned areas. As
a result, left central Laramie county, east Platte county, and
Bordeaux in a watch to see if the NAM can come into better alignment
with the GFS to determine if a mountain wave signature will emerge
with both models.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 140 PM MST Tue Feb 4 2025

Thursday appears to be a transition day between the upper level
trof in the north central U.S., subtle upper level ridging over
northern Rockies and a progressive upper level trof over the
Pacific northwest. This will put the eastern half of our
forecast area in confluent flow (700-500mb) which will most
likely induce brisk winds through Thursday morning. We did bump
up wind speeds across areas mainly east of the I-25 corridor on
Thursday morning, but these winds should diminish somewhat in
the afternoon as the upper level trof in the north central U.S.
begins to depart into the Great Lakes region. Meanwhile, high
clouds are expected to start spilling into the area from west
to east Thursday afternoon and Thursday night as a good Pacific
fetch of moisture starts to push into the area. The
deterministic models including some of the ensembles are hinting
at the potential for some isentropic lift to develop along and
north of a warm front around Converse and Niobrara county on
Thursday night. As a result, this area could experience some
light to moderate snowfall on Thursday night into Friday morning
with the potential for a couple inches of snowfall and result
in some minor impacts.

Gusty winds are expected to develop once again on Friday into
Saturday as the next shortwave moves into the region. Ahead of
this shortwave, temperatures will most likely be on the mild
side along and east of the I-25 corridor due to downslope flow.
However, these warmer temperatures will be shortlived as a
shortwave swings through the area along with its associated
frontal boundary. Behind this front, there is a potential for
snowfall, but the snowfall will be a quick hitter. The greatest
potential will be over the mountains where strong
orographics/instability will be possible on Friday night.
Outside of these areas, snowfall amounts will most likely be
more limited, due to downslope affects.

The remainder of the weekend is expected to be chilly with
well below temperatures. This is in response to a polar low
stationed over the northwest territory which will most likely
keep us in the icebox through early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1005 PM MST Tue Feb 4 2025

MVFR to IFR ceilings will continue at SNY and possibly AIA this
evening as moist easterly upslope remains in place. These lower
ceilings should scatter out later tonight toward sunrise on
Wednesday. Elsewhere expect high cirrus clouds with windy
conditions. Light snow is possible at RWL later this morning
with brief VIS and CIG drops possible through noon. Expect
gusty surface winds area- wide.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 8 AM to 8 PM MST Wednesday for WYZ101-
     116-117.
     High Wind Warning from 5 AM to 11 PM MST Wednesday for WYZ104.
     High Wind Watch from 8 AM MST Wednesday through Wednesday
     evening for WYZ106-107-118.
     High Wind Warning from 5 AM to 5 PM MST Wednesday for WYZ109-
     110.
NE...None.

&&

$$

SHORT TERM...MRD
LONG TERM...REC
AVIATION...MAC