273
FXUS65 KCYS 092057
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
257 PM MDT Sun Mar 9 2025

.KEY MESSAGES...

-  Critical fire weather conditions expected over the High
   Plains along & south of the North Platte River Valley Monday.

-  Strong, gusty winds will return to the wind prone areas
   tonight through Monday.

-  The next storm system will arrive late Thursday into early
   Saturday, bringing strong winds and a chance for
   precipitation.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 300 PM MDT Sun Mar 9 2025

Mild and dry weather will dominate through the middle part of
the week. Currently, it`s a very nice day across the forecast
area with mostly sunny skies and mild temperatures. The southern
High Plains have surged into the lower 60s, while areas to the
north and west with lingering snow cover remain a little bit
cooler. However, melt is likely proceeding rapidly in these
areas.

The axis of a strong upper level ridge will move over the area
tonight into Monday, but it will begin to be flattened by a
shortwave trough passing well to our north. While no
precipitation is expected from this system, it will help to
increase the temperature and low-level height gradient across
the area, leading to a period of increased winds over the
northern Rockies. MSLP gradients will also be on the increase
ahead of the associated surface trough expected to sweep through
late Monday afternoon. As a result, strong winds are on track
for tonight into Monday, at least for the wind prone areas.
While pressure and height gradients are fairly marginal, 700-mb
winds over 50-knots and a strong subsident signal over the
terrain provides more confidence in higher winds. This extends
to Converse County, where the subsident signal and potential for
mountain waves gave enough confidence to upgrade the watch to a
Warning. Models are fairly consistently showing mid-level ascent
over Platte County, likely the upward side of a standing
mountain wave. With this hovering over I-25 in Platte County,
there was not enough confidence to upgrade that zone. However,
we still need to keep an eye for occasional wave breaking
spilling to the highway, in addition to the afternoon period
when the passing cold front will pull the surface trough east.
There are a few other zones we will need to keep an eye on,
including the Interstate 80 summit, and central/northern Carbon
county. For the former, the wind direction is somewhat
unfavorable, and cross-barrier MSLP gradient a little low for
high winds. For the latter, 700-mb winds only around 40 to 45
knots and an unimpressive MSLP gradient keep confidence too low.
Still, both should be considered again with the next forecast
update. In addition to the high winds for the wind prone areas,
increasing wind speeds will lead to critical fire weather
conditions over the southern High Plains without snow cover.
More details on this can be found in the fire weather section
below. The main piece of uncertainty with the fire weather
concerns is the potential for high level mountain wave cirrus
clouds to develop, which could inhibit mixing and keep RH a
touch above critical.

Winds should ease Monday evening, but it will remain breezy for
several more days. Behind the cold front and with weaker westerly
downslope flow for the High Plains, expect highs Tuesday to be
slightly cooler than Monday as largely zonal flow continues
aloft.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Issued at 300 PM MDT Sun Mar 9 2025

Wednesday...Low amplitude ridging and westerly flow aloft prevails.
With downslope west winds and 700 mb temperatures near 1 Celsius,
maximum temperatures will be in the upper 40s to lower 50s west of I-
25, with upper 50s to mid 60s east of I-25.

Thursday...One last mild day expected as the flow aloft turns
southwest ahead of the next approaching shortwave trough. Scattered
orographic rain and snow showers moves over our Snowy and Sierra
Madre Ranges, with dry conditions elsewhere. Similar temperatures to
Wednesday with 700 mb temperatures near 2 Celsius.

Friday...The progressive upper trough aloft moves into southern
Colorado Friday morning, then to eastern Nebraska by evening, with a
strong cold frontal passage and plenty of wraparound snow across our
counties during the day. Boosted winds as the low and mid level
gradients increase markedly, especially with strong cold air
advection in the wake of the cold front.

Saturday...Continued quite windy as the progressive flow aloft
continues with strong northwest flow. Looks like enough low and mid
level moisture in the flow aloft to produce orographic snow showers
for our Snowy and Sierra Madre Ranges, and lesser so for our
northern and southern Laramie Ranges. Continued blustery with 700 mb
temperatures near -10 Celsius yielding high temperatures from the
mid 30s to mid 40s.

Sunday...The flow aloft backs to westerly, inducing surface lee
troughing development, and a decent warming trend as 700 mb
temperatures near 0 Celsius yield maximum temperatures from the
lower 40s west of I-25, to the upper 40s to mid 50s east of I-25.
Looks like enough moisture again for a continuation of orographic
snow showers for our Snowy and Sierra Madre Ranges.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1131 AM MDT Sun Mar 9 2025

West flow aloft will continue. Skies will be mostly clear with
occasional scattered clouds near 15000 feet. Low level wind
shear occurs at Laramie and Cheyenne from 04Z to 15Z, and at
Chadron, Alliance and Scottsbluff from 00Z to 15Z. Winds will
gust to 30 knots at all terminals until 00Z, to 38 knots at
Rawlins and Laramie after 04Z, and to 32 knots at Cheyenne and
the Nebraska terminals after 14Z Monday.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Sun Mar 9 2025

Critical fire weather conditions are expected over portions of the High
Plains without existing snow cover on Monday. Warm temperatures reaching
the 60s to low 70s on Monday will produce afternoon RH between 10 and 15
percent. Additionally, west winds at 15 to 30 mph gusting 35 to 45 mph are
anticipated. A few gusts as high as 55 MPH will be possible in Laramie
county. Areas north of the North Platte River valley can still expect
gusty winds and low humidity, but the lingering snow cover should keep
conditions outside of critical. Warm, dry, and breezy weather will continue
through Thursday producing elevated fire weather conditions.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from 11 AM to 7 PM MDT Monday for WYZ430-431-
     433.
     High Wind Warning from 3 AM to 6 PM MDT Monday for WYZ101.
     High Wind Warning from 6 PM this evening to 6 PM MDT Monday
     for WYZ106.
     High Wind Watch from midnight MDT tonight through Monday
     afternoon for WYZ107.
     High Wind Warning from 6 AM to 6 PM MDT Monday for WYZ110.
NE...Red Flag Warning from 11 AM to 7 PM MDT Monday for NEZ436-437.

&&

$$

SHORT TERM...MN
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...MN