Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 180546
AFDCYS

Area Forecast Discussion...Corrected
National Weather Service Cheyenne WY
1030 PM MST Fri Nov 17 2017

.UPDATE...
Issued at 825 PM MST Fri Nov 17 2017

Evening water vapor loop showed the mid/upper level trough axis
from western WY through central UT. Area of snowfall associated
with a shortwave over central WY was moving southeast. Cold front
that moved through the CWA earlier this afternoon extended from
southeast UT across central CO and KS, with an extensive band of
post-frontal precipitation. Mountain SNOTELs indicated another 4-6
inches of snowfall since early this afternoon. Hourly snow rates
have decreased somewhat, with a gradual tapering trend through
midnight. Will be tweaking PoPs and weather grids to account for
the radar trends.

&&

.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
gradients.

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 06Z TAFS through 06Z Saturday evening)
Issued at 1030 PM MST Fri Nov 17 2017

IFR-LIFR VIS/MVFR CIG in moderate snow and wind gusts to 45 KT will
impact KLAR and KCYS through 08Z. A period of MVFR CIG is forecast
at KSNY and KAIA until 09Z. VFR conditions will prevail after 09Z.
Gusty NW winds of 25-35 KT will continue through Saturday afternoon.

&&

.FIRE WEATHER...
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.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until 11 PM MST this evening for WYZ112-
114.

     Winter Weather Advisory until 11 PM MST this evening for WYZ110-
     115-116.

NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...MAJ
FIRE WEATHER...TJT/GCC



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