646
FXUS65 KCYS 231718
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1018 AM MST Sun Feb 23 2025

.KEY MESSAGES...

- A long duration wind event is expected through at least
  through Tuesday in the wind prone areas. Winds may spill into
  adjacent zones Sunday PM through Tuesday PM.

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

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 348 AM MST Sun Feb 23 2025

Clear skies overhead tonight as winds continue to crank up across
the wind prone regions and adjacent areas. Arlington, the I-80
Summit, and the Foothills have been hitting high wind criteria
fairly consistently for the last few hours, with Bordeaux slowly
coming up as well. Temperatures are quite warm tonight, with 10Z
temperatures in the low- to mid-30s area wide with a couple
locations in the upper-20s. Strong winds are not expected to
decrease anytime soon and will only continue to increase throughout
the day today.

Strong winds continue to be the main concern in the short term
period, with multiple locations already hitting high wind criteria
overnight tonight. The upper-level ridge punching into southern
Canada is visible on GOES-East IR satellite tonight. This ridge
will continue to push across southern Canada with the base of the
ridge remaining stationary near the Four Corners Region due to a
lack of any 500mb anticyclonic vorticity advection. Northwesterly
flow aloft is forecast to remain overhead throughout the next
several days, further favoring multiple systems to push through the
region for the end of the weekend into the early work week. A couple
modest strength 500mb vorticity lobes will traverse overhead today,
but with fairly weak moisture due to downsloping winds,
precipitation chances are not expected anywhere outside of the
mountains later today into the evening hours. The 700mb system
producing these strong winds on Sunday will slowly push over
southern Canada, just ahead of the incoming upper-level ridge.
However, the system will be fairly strong, despite only showing up
in models as an open shortwave. A 65 to 70kt 700mb jet is forecast
to develop over central Montana due to the strengthening height
gradients at 700mb. As a result to the strengthening gradients from
this fairly strong system, the 700mb jet over the CWA will increase
to around 65 to 70kts by Sunday evening, leading to the first period
of 75 to 80mph gusts likely in the wind prone regions and 65 to
70mph gusts in adjacent areas. In combination with the strong 700mb
jet overhead during this time, surface pressure gradients will be at
their maximum for Sunday, due to a surface trough pushing across
northeastern portions of the CWA. 850mb Craig to Casper gradients
will increase into the low- to mid-80s with 700mb gradients not far
behind in the mid-50s. In-house random forest guidance increases to
around a 85 to 90% probability for high winds at both Arlington,
Bordeaux, and Northern Carbon County with areas like the I-80 Summit
closer to 65 to 70% probability for high winds. The GFS indicates
surface winds approaching 35kts or more along the Laramie Range,
including near the I-80 Summit. The FV3 model additionally shows
surface winds around 35kts along the I-80 Summit and the Laramie
Range, with similar values near Arlington, Bordeaux, northern Carbon
County, and portions of the South Laramie Range Foothills. Very
strong downward omega values will be present across the Laramie
Range and the Snowy Range, leading to the "perfect storm" for very
strong winds across much of southeast Wyoming. Did decide to expand
the high wind watches to include Niobrara County and the western
column of counties in western Nebraska. With winds as strong as
models are expected, surface gusts exceeding 55 to 60 mph should
fairly easily spread eastward out of the wind prone into adjacent
areas. Additional, with a 50kt 800mb jet across portions of the
Panhandle, very strong surface winds are further favored. However,
due to some uncertainty on whether these winds will mix all the way
down to the surface kept these counties in a watch rather than
upgrading straight to a warning. Will let day crew take another look
at these locations to determine whether or not short-fuse upgrade
will be needed later today.

After a period of strongest winds Sunday night into Monday morning,
a secondary system will push across Montana and South Dakota
prompting strong winds to continue throughout the day Monday.
Strongest wind chances look to be Monday morning as a 60 to 65kt
700mb jet remains over the CWA. An 80kt 700mb jet will be associated
with the second system, due to the strong height gradients
associated with it. As a result, height gradients across the CWA
will only continue to increase as this system moves off to the
northeast of the CWA early Monday morning into the late morning
hours. A brief lull looks possible Monday afternoon towards the
Monday evening/Tuesday morning hours, but will quickly increase
again Tuesday morning throughout the day Tuesday, with the final
surge of winds looking to finally subside late Tuesday night into
the early morning hours Wednesday. Once again, Craig to Casper
gradients will be well into the 60s and 70s throughout the day
Monday into early Tuesday morning, with strong downward omega values
across the Laramie and Snowy Ranges. Maximum downward omega values
develop along the Laramie Range in the early morning hours Tuesday
and continue into the afternoon hours, providing the second major
threat throughout this entire wind event. See long term discussion
for more about Tuesday afternoon into the evening hours.

Thankfully, with strong downsloping winds, temperatures will be
quite nice over the next few days with highs in the 50s and 60s east
of the Laramie Range and 40s west of the Laramie Range. A fairly
diffuse cold front will push through the region Monday afternoon
into the evening hours, but will likely only drop temperatures on
Tuesday a couple degrees. However, with the additional forcing from
the front, could see some mountain snow chances Monday morning
through Monday evening. Sub-advisory amounts of snow are currently
expected for both the Sierra Madre and Snowy Ranges, but the Sierra
Madres will approach that 6 inch march over the day.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 348 AM MST Sun Feb 23 2025

Slightly negative tilted shortwave is expected to quickly pass
through Wyoming and Nebraska panhandle during the course of the day
Tuesday. At the base of this shortwave, the models/ensembles are
showing a significant low level jet (800-750mb) 50 to 60kts slicing
through southeast Wyoming and parts of the Nebraska panhandle on
Tuesday afternoon. There is also quite a bit of mountain wave
activity with this shortwave which will allow for impressive wave
breaks especially on the lee side of Laramie Range. This combined
with good subsidence and mixing will yield to fairly strong winds on
the east side of the Laramie Range late Tuesday morning into the
afternoon. In fact, we would not be surprised to see some gusts up
to 70 mph, especially in Bordeaux and points east where this axis of
high winds will be in place. Further south and north, it will be
still be quite windy with some gusts of 50 to 60 mph. Latest model
trends have been fairly consistent with this corridor of high winds,
but we will need to watch how this shortwave evolves over the next
day or so.

West of the Laramie Range, wind speeds may be a bit less but still
windy during the course of Tuesday morning. Places like Rawlins, Elk
Mountain and Rawlins will most likely experience the low level jet
and subsidence during the course of the morning, but this jet should
begin to depart the area by mid afternoon. Either way, it looks like
a windy day across most of the forecast area.

The frontal boundary associated with this wave is expected to enter
the northern portions of the forecast area on Tuesday afternoon,
which is expected to shift the wind direction more towards the
northwest. Although, it may still continue to be windy, due to
plenty of subsidence developing behind the front. This may favor an
extended period of high winds into the early evening as this front
passes through areas east of the Laramie Range. Therefore, the high
wind watches/warnings continue through that that time frame. The
good news is these winds should begin to taper off late Tuesday
night as surface high pressure builds over the area with
temperatures tumbling into the 20s.

The upper level ridge is expected to begin building over the area
through the remainder of the week. After a cooler day on Wednesday
(30s and 40s), temperatures will once again rebound to the 40s and
50s for the remainder of the week due to strong downslope flow as
the upper level ridge slides south of Wyoming.
Dry conditions will also be the rule through the remainder of the
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1018 AM MST Sun Feb 23 2025

VFR conditions prevail through this TAF period. The area of high
pressure of northwest Colorado remains strong throughout the day
as the 700mb jet (45-60kts) continues to reside overhead. This
will keep the stronger wind gusts persisting throughout the day
and evening for the Southeast Wyoming terminals and KBFF.
Starting at 01z low level wind shear will start to develop with
40-50kts at all sites. Moisture and weak forcing creates some
snow chances for KRWL after 06z with the best chances between
10z through 14z. However, given the dry atmosphere not confident
enough to put light snow in the TAF.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 11 PM MST Tuesday for WYZ101-104>107-
     109-110-116-117.
     High Wind Watch through Tuesday evening for WYZ102.
     High Wind Warning until 11 PM MST Tuesday for WYZ108-118.
     High Wind Watch through Tuesday evening for WYZ115.
     High Wind Watch from Monday morning through Tuesday evening
     for WYZ119.
NE...High Wind Watch from 2 PM MST this afternoon through Tuesday
     evening for NEZ019-095-096.
     High Wind Watch from 5 PM MST this afternoon through Tuesday
     evening for NEZ020-054.

&&

$$

SHORT TERM...AM
LONG TERM...REC
AVIATION...MM