Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 172138

Area Forecast Discussion
National Weather Service Cheyenne WY
238 PM MST Fri Nov 17 2017

.SHORT TERM...(This evening through Saturday night)
Issued at 230 PM MST Fri Nov 17 2017

Current observations and webcams across southeast Wyoming show
snowfall mainly west of Interstate 25, with mainly rain showers
further east and even a few lightning strikes along and south of
Interstate 80 earlier this afternoon. Main surge of cold air looks
like its starting to move into the area across Carbon and Albany
counties at this hour, with one quarter mile to one half mile
visibilities and falling temperatures from Rawlins to Laramie.
Current headlines look ok, with difficult travel conditions around
the Elk Mountain and Arlington areas. Will have to keep an eye on
the I-80 summit and Laramie valley over the next 3 to 6 hours with
this next area of moderate snowfall, if road temperatures fall
quickly, may need additional Winter Weather Advisories for these
locations as well with 2 to 4 inches of snow expected. Further
east, most areas across the High Plains have been in the warm
sector of the frontal system, which has been stationary across the
area, so even as the rain changes to snow this evening,
accumulations should be less than two inches on grassy surfaces.
Wind concerns will continue to subside tonight, but can`t rule
out some blowing snow across the wind prone areas that are
receiving snowfall this afternoon. Precipitation will gradually
come to an end from northwest to southeast after midnight.

For the beginning of the weekend, models show northwest flow aloft
on Saturday with colder than average temperatures in the 30`s to
low 40`s across most of the region. West to northwest winds will
be gusty for most of the day with sustained winds between 15 to 30
mph and gusts up to 45 mph. It will be dry with no precipitation
expected through Saturday night.

.LONG TERM...(Sunday through Thursday)
Issued at 307 AM MST Fri Nov 17 2017

Sunday...A decent warming trend begins as the flow aloft backs to
almost straight westerly with a surface lee trough forming. With a
bone dry airmass, no precipitation is anticipated. Will stick close
to guidance maximum temperatures.

Monday...Fast moving shortwave trough aloft approaches from southern
Idaho in the afternoon with strong zonal flow aloft helping to
produce a windy day. Continued mild like Sunday based on thicknesses
and 700 mb temperatures. By early evening, chances for showers will
spread across Carbon County in the moist orographic flow aloft.

Tuesday...Fast moving shortwave trough aloft moves southeast into
Colorado by dawn, with fast northwest flow aloft across our counties
in the afternoon. Drying out in the afternoon behind the shortwave
trough aloft and breezy to windy per progged surface to 700 mb

Wednesday...Another warming trend begins with rising heights and
thicknesses on northwest flow aloft. Flow at the surface and aloft
remains strong enough for windy conditions, and possible high wind
criteria across our wind prone locations.

Thanksgiving...Mild temperatures continue as the flow aloft backs to
westerly with relatively high heights aloft...5780 meters at 500 mb,
along with downslope warming. Low and mid level moisture look too
scant for any precipitation.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1057 AM MST Fri Nov 17 2017

The main concern with this TAF issuance is the wind direction at
the Wyoming TAF sites today. Latest surface analysis is showing
that the models are struggling with the surface pressure fields.
As a result, we are seeing the models struggling with the wind
fields. Based on the latest surface analysis, we would anticipate
a later cold frontal passage. It looks like frontal boundary
should pass through this evening with some short-lived post
frontal precip. following behind it.


Issued at 138 PM MST Fri Nov 17 2017

Temperatures will be colder tonight and Saturday behind a frontal
system that will slowly progress eastward. No Fire Weather
concerns this weekend and next week due to precipitation today
along with colder temperatures. It will be drier next week with
mild temperatures each day.


WY...Winter Storm Warning until 11 PM MST this evening for WYZ112-114.

     Winter Weather Advisory until 11 PM MST this evening for WYZ110.



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