Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 111727

Area Forecast Discussion
National Weather Service Cheyenne WY
1027 AM MST Sun Feb 11 2018

.SHORT TERM...(Today through Tuesday)
Issued at 230 AM MST Sun Feb 11 2018

Arctic cold front was analyzed from eastern ID across southwest WY
to west of the CO Front Range. Center of surface ridge was situated
over the central Great Plains. Skies were clear, with the leading
edge of high clouds entering northern WY. Winds were light, except
along the I-80 corridor between Rawlins and Cheyenne where westerly
winds were gusting between 20 and 35 mph. Temperatures were in the
single digits and teens.

00Z short range models/ensembles continue good run-to-run consistency
with the large scale pattern. Northwest-west flow aloft today backs
to the southwest Monday as split flow develops across the western
CONUS. Closed upper low over NV/CA retrogrades southwestward offshore
with progressive northern stream shortwave trough tracking east across
the northern Great Plains and Upper Midwest Tuesday.

The Arctic front to the west of the CWA surges eastward as a warm
front today, with warming temperatures from gusty downslope westerly
winds. Winds may gust as high as 55 mph through the wind-prone areas
including Arlington and Bordeaux, mainly this morning with 700mb
winds near 45 kt and CAG-CPR 700/850mb height gradients 50-55 meters.
High temperatures this afternoon will be 15-20 degrees warmer compared
to yesterday with 20s and 30s.

The warmup will be brief as the Arctic cold front surges back to
the southwest tonight and Monday morning as a 1046mb surface ridge
builds southeast into the northern Great Plains and Midwest. Snow
develops along and behind the front from central WY to western SD
late tonight and spreads southward across the remainder of the CWA
Monday. Snowfall will be light (generally less than an inch), except
over the Snowy/Sierra Madre Range mountains where orographic lift
may produce four to eight inches, heaviest over the Sierra Madre Range
Monday and Monday night. Since this occurs during the 3rd and 4th
forecast periods, decided to not issue a Winter Weather Advisory
and let the next shift glean the 12Z models to refine timing and
snow accumulations. It will be colder Monday with highs from the
teens north to the 20s and 30s south.

Cold front quick retreats east of the CWA Tuesday with warmer
temperatures courtesy of increasing downslope westerly flow. Highs
Tuesday afternoon will range from the mid 30s to mid 40s. The
pressure gradient tightens beginning Tuesday afternoon with gusts
to 45 mph along and west of the Laramie Range.

.LONG TERM...(Tuesday night through Saturday)
Issued at 230 AM MST Sun Feb 11 2018

Generally mild weather expected over the CWA during this period with
a west to wnw upper flow bringing a respite to the Arctic air surges.
Still appears there will be a period of strong winds in the wind-
prone areas Tuesday night and Weds as lee troughing deepens over the
high plains in response to an upper trough approaching from southwest
Canada. This trough will move into the plains early Thursday and push
a Pacific cold front across the CWA as well as bring some snow showers
to mainly the higher mtns Weds night into Thursday. Cooler across the
CWA Thursday then a return to milder and mainly dry weather Friday
through Saturday.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1024 AM MST Sun Feb 11 2018

Wyoming TAFS...VFR until 09Z at Rawlins and Laramie, then MVFR.
VFR at Cheyenne until 08Z, then IFR.

Nebraska TAFS...VFR at Chadron, Alliance and Sidney until 06Z to
08Z, then IFR. VFR at Scottsbluff until 06Z, then MVFR.


Issued at 230 AM MST Sun Feb 11 2018

The Arctic cold front poised to the west early this morning will
surge eastward today, bringing breezy to windy conditions and warmer
temperatures to the districts. The warmup will be short-lived
however as the cold front moves back to the southwest into southeast
Wyoming and western Nebraska tonight and Monday morning. Snow will
develop late tonight across east central Wyoming and northwest
Nebraska and spread south across the remainder of the districts
Monday. Snowfall will be light, except over the Snowy and Sierra
Madre range mountains where four to eight inches may accumulate
through Monday night. The cold front retreat well east of the area
Tuesday, with windy and warmer weather through mid- week.




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