Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 260619
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1119 PM MST Fri Nov 25 2016

.SHORT TERM...(This evening through Sunday night)
Issued at 230 PM MST Fri Nov 25 2016

Challenges deal with strong winds and snow across our western
zones Sunday into Monday.

Currently...Surface low pressure being analyzed up near Gillette
this afternoon. Not really impacting southeast Wyoming and
Nebraska Panhandle so far, but we are starting to see an increase
in cloud cover. Winds have been elevated across much of the area
with gusts in the upper 30s near Arlington and north Laramie
range. Downsloping winds off the Laramie Range has raised
temperatures into the mid 50s here in Cheyenne with humidities
down around 10 percent. Fortunately winds are fairly light.

Water Vapor imagery showing a rather potent low pressure system
off the coast of Oregon and northern California. We are going to
need to watch the track of this low pressure system into the
weekend.

Both the GFS and latest ECMWF run shows this low tracking into
southern California Saturday afternoon, then ejecting northeast
into Colorado Sunday morning. Carbon County looks to be on the
favorable left quadrant of a 130+ knot 250mb jet beginning Sunday
morning and persisting through the day. Both the GFS and ECMWF has
snow developing over the Snowy and Sierra Madre ranges as early
as 12Z Sunday, persisting into Monday. Strong 850/700mb Craig to
Casper height gradients being forecast on both the local strong
wind forecast products beginning Sunday around 18Z Sunday.

With the persistent snow over the mountains and increasing
pressure gradients, decided to go with a Winter Storm Watch for
the Snowy and Sierra Madre Ranges as well as the Arlington zone on
Interstate 80. Snow and strong winds will continue into Tuesday.

.LONG TERM...(Monday through Friday)
Issued at 255 PM MST Fri Nov 25 2016

Significant change to the overall weather pattern is expected for
next week with much colder temperatures expected in the
foreseeable future. These temperatures will be a significant
deviation from conditions over October and earlier this month.
Models and ensembles show a long wave upper level trough moving
over the western third of the United States late Sunday. This
feature is expected to remain nearly stationary or shift
slightly to the east through the week...and then the longwave
trough may actually retrograde westward by next weekend.
Thankfully...no major storm systems appear to be on the horizon as
the Polar jet rapidly dives southward towards the Mexico/U.S.
border by late next week. With the storm track so far south...any
snowfall will have to initiate from limited dynamic forcing and
weak shortwave disturbances aloft along with little low to
midlevel moisture. Tuesday through Thursday will be pretty cold
and blustery days with highs struggling to reach the mid 20`s to
mid 30`s across the whole forecast area along with gusty winds
during each day. Will have to watch some of the wind prone areas
for locally strong gap winds each morning as the llvl pressure
gradient will increase mainly due to high pressure to the west of
the continental divide. Although no significant systems are
expected through late next week...periods of snow across the
mountains will result in light to moderate accumulation.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1117 PM MST Fri Nov 25 2016

VFR conditions prevail overnight. Gusty winds should develop again
on Saturday for terminals near the mountains.

&&

.FIRE WEATHER...
Issued at 123 PM MST Fri Nov 25 2016

Windy conditions expected to continue into the weekend as low
pressure approaches the area from the west. Wind prone areas will
gust into the mid 40 MPH range with afternoon humidities falling
into the mid teens along the Interstate 80 corridor from Sidney to
Cheyenne Saturday. Fortunately we have seen recent snowfall that
should help ease fire weather concerns. Next storm system moves
into the area Sunday with snow becoming widespread west of the
Laramie Range during the say Sunday and into areas east of the
Laramie Range Monday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Watch from late Saturday night through Monday
     afternoon for WYZ112-114.

     Winter Storm Watch from Sunday morning through Monday afternoon
     for WYZ110.

NE...None.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...CLH
FIRE WEATHER...GCC



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