Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 130952

Area Forecast Discussion
National Weather Service Cheyenne WY
252 AM MST Wed Dec 13 2017

.SHORT TERM...(Today through Friday)
Issued at 230 AM MST Wed Dec 13 2017

Today...Next fast moving positively tilted shortwave trough aloft
scoots southeastward into western Wyoming this afternoon, with a
chance of light snow this afternoon over much of Carbon County and
the northern Laramie Range, with dry conditions elsewhere. Progged
gradients suggest breezy to windy conditions this afternoon across
far eastern Wyoming and especially over the western Nebraska
Panhandle. Cooler today in the wake of the passing cold front.

Tonight...Progressive shortwave trough aloft moves into Colorado,
and with adequate low and mid level moisture, will produce scattered
to numerous snow showers along and west of Interstate 25, with the
greatest POPs over the Northern Laramie, Snowy and Sierra Madre
Ranges, where 3 to 5 inches of snow will fall. Dry further east.

Thursday...Breezy to windy, raw day expected with cold temperatures
and highs only in the 30s, with progged surface to 700 mb gradients
producing northwest winds of 25 to 35 mph gusting to 40 to 50 mph
over far eastern Wyoming and the Nebraska Panhandle.

Thursday night...Dry, mostly clear and seasonably cold night.

Friday...Rather pronounced warming trend expected as the flow aloft
backs to northwest, and heights and thicknesses increase markedly,
with downslope west winds helping maximum temperatures to soar into
the mid 40s to upper 50s at lower elevations along with breezy to
windy conditions.

.LONG TERM...(Friday night through Tuesday)
Issued at 230 AM MST Wed Dec 13 2017

Strong winds likely Friday night especially out by Arlington. GFS
700mb winds across eastern Carbon/western Albany Counties right
around 55kts. Craig to Casper 850/700mb height gradients both
above 60mtrs til about 06Z Saturday off the GFS. May stick around
a little longer than what the high wind guidance is showing as
GFS 700mb winds stay above 50kts til 12Z Saturday. Whats causing
these strong winds is a cold front approaching from the west and

This front begins to produce snow showers Saturday morning as it
sags across southern Wyoming. Snow begins out across Carbon and
Converse Counties as early as 12Z Saturday, becoming fairly
widespread during the morning hours. Did undercut temperatures for
Saturday as GFS 700mb temperatures fall to -12C by the afternoon.
Would think all precip would be in the form of snow. Could be
looking at some accumulations across the mountains. GFS QPF over
the north Laramie Range approaching .5 inches as well as the Snowy
Range. Later shifts will need to consider the need for winter
headlines. Fairly fast movement of the front through the area with
snow ending from north to south by early Sunday morning. This may
limit snow accumulations some as most of the snow will fall
during the day.

Going to stay cold as 700mb temperatures stay well below freezing
til at least Wednesday next week. That will likely be our next
high wind event as GFS 700mb winds again increase to 45-50kts.

Long term guidance continues to show an arctic boundary sagging
south towards the end of next week that we need to be watching
closely. GFS 700mb temps down as low as -20C across Converse and
Niobrara Counties next Thursday.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday evening)
Issued at 1045 PM MST Tue Dec 12 2017

Clouds will increase and lower from west to east tonight through
Wednesday as a clipper system and cold front approach from the
northwest. CIGS will remain VFR, except lowering to MVFR in light
snow along and west of the Laramie Range Thursday evening. The
mountains wil become obscured as well. It will be breezy to windy
east of the Laramie Range, with northwest winds gusting between 25
and 35 KT, especially Wednesday.


Issued at 142 AM MST Wed Dec 13 2017

Minimal concerns most days, except for low humidities near 15
percent Friday afternoon across far southeast Wyoming and the
southern half of the Nebraska Panhandle.




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