Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 051102

Area Forecast Discussion
National Weather Service Cheyenne WY
402 AM MST Mon Dec 5 2016

.SHORT TERM...(Today through Tuesday night)
Issued at 402 AM MST Mon Dec 5 2016

Today...Winds over the I-80 summit and near Bordeaux in Platte
county continue to decrease, thus the 8 am ending to the high wind
warning looks on track. Could have likely dropped the high wind
warning earlier, though would prefer to err on the side of caution.

Attention then turns to the approaching strong cold front expected
to pass west to east with steady or slowly falling temperatures in
its wake this afternoon. Baroclinic band snows and orographic snow
expected to start over the Snowy and Sierra Madre Ranges and
combined with the blustery winds, our inherited winter weather
advisory there looks on track, as well as in the Arlington and Elk
Mountain locations.

Tonight...Much colder air will continue to filter into the region in
the wake of the initial cold front and will trend towards the colder
guidance low temperatures. Snow will decrease in areal coverage as
low and mid level moisture decreases with most snow confined to the
mountains and nearby locations.

Tuesday...Next shortwave approaches from southwest Wyoming with
snows developing and increasing in coverage along and near the
Colorado state line from southern Carbon county eastward to Laramie
county especially looking at the 500-300 mb and 700-500 mb layer
quasigeostrophic forcing. Models similar in showing snow continuing
to increase in coverage in the afternoon, mainly south of a Rawlins
to Scottsbluff line with the greatest coverage across southeast
Wyoming from Laramie to Cheyenne. Could see some localized 2 to 4
inch snowfall accumulations from a powdery type snow, so we may need
localized winter weather advisories at lower elevations. Even colder
as deeper cold air filters into the region. Have stuck close to the
colder guidance high temperatures.

Tuesday night...As the shortwave moves across far southeast Wyoming
and northeast Colorado, widespread light snow will continue to the
south of a Laramie to Scottsbluff line, with lesser snow coverage
elsewhere. With the cold temperatures, the snow will likely be in
the 20 or 25 to 1 ratio, and quite powdery.  Stuck close to the
colder guidance minimum temperatures.

.LONG TERM...(Wednesday through Sunday)
Issued at 402 AM MST Mon Dec 5 2016

Strong Canadian high pressure and very cold airmass will move
into the Rockies on Wednesday while cold, cyclonic flow remains
overhead. Snow will steadily end through the day as dynamic lift
and upslope flow diminish. It will be quite cold as high temps
will only be in the single digits to low teens within the Canadian
airmass. Expecting temps to then drop below zero over much of the
forecast area Wednesday night as winds lighten. Wind chills could
plummet to readings between minus 20 and minus 30 (or less) even
with relatively light winds in place (5-10 mph for many
locations). Thankfully, heights aloft will begin to rise on
Thursday and Thursday night, bringing warmer temperatures back to
our area. Along with it tho will be strong winds in the wind prone
areas along and west of I-25 starting late Thursday. Fast and
energetic zonal flow looks to move overhead on Friday and Saturday
maintaining strong winds in the wind prone areas. The likelihood
for orographic snow will increase through this time as well, with
moderate accumulations a good possibility up in the higher peaks.
Both snow and wind should diminish somewhat Sunday and Sunday
night as the upper jet shifts south and east of us.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1026 PM MST Sun Dec 4 2016

Snow will spread east into Carbon County overnight, with MVFR
cigs/vis at RWL and SAA airfields by 12Z. The mountains will be
obscured by snow and low cigs. Snow showers may impact LAR after
15Z, and AIA and CDR after 17Z. VFR cigs will prevail elsewhere.
Strong and gusty pre-frontal winds will continue through Monday
morning across southeast WY, then shift into the west and northwest
and remain rather gusty areawide through the afternoon.


Issued at 402 AM MST Mon Dec 5 2016

No concerns due to projected humidities and falling snow over the
mountains today, and over the lower elevations Tuesday afternoon
and Tuesday night.


WY...Winter Weather Advisory until 8 PM MST this evening for WYZ112-

     High Wind Warning until 8 AM MST this morning for WYZ106-110-116-

     Winter Weather Advisory from 8 AM this morning to 8 PM MST this
     evening for WYZ110.



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