Area Forecast Discussion
Issued by NWS Cheyenne, WY

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396
FXUS65 KCYS 020450 AAA
AFDCYS

Area Forecast Discussion...Updated Aviation
National Weather Service Cheyenne WY
950 PM MST Thu Dec 1 2016

.UPDATE...
Issued at 921 PM MST Thu Dec 1 2016

Weak shortwave evident in water vapor imagery tracking east across
central WY this evening. This feature is aiding in the development
of snow showers, mainly along and west of the I-25 corridor. The
latest HRRR reflectivity data supports this trend tonight. Did
increase PoPs into northern Carbon and western Converse counties
based on HRRR.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 226 PM MST Thu Dec 1 2016

Light snow showers continue over the high country in southeast
Wyoming this afternoon as a piece of vorticity moves overhead ahead
of the main shortwave trough digging south along the Rockies.
This trough is not really moving all that fast, in fact will
elongate northeast-southwest over the next 24hrs, effectively
remaining overhead through Friday. Therefore, may see light snow
showers continue over the mountains within persist lift and
moisture. Not anticipating much accumulation in the mountains,
perhaps a couple inches, but elsewhere should only be a light
dusting. Temperatures will be a few degrees colder on Friday with
the trough overhead, with relatively light winds continuing
through this time.

On Friday night, a disturbance moving southeast across Wyoming
on the nose of a strong northwest jet will nudge the stagnant
trough to the east. High pressure building in from the west on
the wake of this disturbance, combined with pressure falls
expected to occur across the plains ahead of the trough will
strengthen the sfc pressure gradient rapidly across southeast
Wyoming Friday night. As we approach sunrise, expect winds to
become quite strong across the wind prone areas, mainly the gap
areas near Arlington and Bordeaux. Should be an active mountain
wave too, so will have to see whether high winds occur elsewhere,
such as Vedauwoo, Buford and other nearby locations. Issued a
High Wind Watch for Arlington & Bordeaux as This us a favorable
pattern for strong winds in these locations. Model progs of
800-700 mb winds look marginal, ranging 40-50 kts, so expecting
only a marginal High Wind event as sfc gusts should be around 60
mph. The rest of Saturday will be breezy across the region with
the gradient remaining fairly tight through the day. With
downslope winds in place, along with rising heights aloft, it
should be about 5 degrees warmer. Some midlevel moisure moving in
from the west, combined with the westerly upslope flow could spark
off some snow showers Saturday afternoon over the Snowy and Sierra
Madre mountains.

.LONG TERM...(Saturday night through Wednesday)
Issued at 226 PM MST Thu Dec 1 2016

Models continue to be in rather good agreement at showing a very
cold airmass moving into the region by early next week.  Zonal flow
aloft will be in place on Sunday, with highs rising into the 40s.
This will be the warmest day as a strong fropa will occur on Monday
in association with a shortwave moving to the north of the CWA.
Orographic snow will begin on Monday over the Sierra Madre and Snowy
Ranges.  A secondary shortwave will amplify into Utah on Monday
night and Tuesday morning.  Large scale lift will increase in areas
near the Colorado Border by Tuesday into Tuesday night.  Will keep
the highest PoPs in areas near Interstate 80.  The ECMWF is slower
than the more progressive GFS.  This will be the coldest air of the
season so far with 700 mb temps dropping to a very chilly -22C by
Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday evening)
Issued at 950 PM MST Thu Dec 1 2016

Periodic snow showers will continue tonight and Friday morning along
and west of Interstate 25. The showers will lower ceilings and
visibilities to MVFR at times at RWL, with mountain obscurations.
Otherwise, cloud cover will increase from west to east, with
ceilings between 5000 and 10000 ft AGL. Light winds will prevail.

&&

.FIRE WEATHER...
Issued at 226 PM MST Thu Dec 1 2016

Minimal fire weather concerns will continue through next week as
cold temperatures will remain over the area. Winds gusting 20 to
30 mph this afternoon along and west of I-25 will ease through
this evening with light winds continuing through Friday. Another
winter storm system set to move into the area Sunday into
Wednesday that may bring widespread accumulating snow.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from late Friday night through Saturday
     afternoon for WYZ106-110.

NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...RJM
LONG TERM...RE
AVIATION...MAJ
FIRE WEATHER...RJM



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