Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 051543

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

Issued at 836 AM MST Mon Dec 5 2016

Updated forecast to expand the Winter Weather Advisory into
Converse county this morning and early afternoon. It has been
snowing all morning along and north of Interstate 25 with maybe an
inch or two on the ground already. Expect snow...moderate to heavy
at continue this morning and ending around noon. Winds
may pick up for a time behind the cold including
wording for blowing snow...which should mainly impact the high
ridges north of Douglas. Conditions should improve by mid

Otherwise...forecast appears on track for most other locations.
Will have to monitor the southern Laramie Range including the I80
summit since snow has been a bit more intense than previously
expected with a strong westerly wind.


.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 12Z TAFS through 12Z Tuesday morning)
Issued at 559 AM MST Mon Dec 5 2016

Snow showers are moving over the high country this morning, likely
bringing KRWL down to MVFR vsbys/cigs thru midmorning and perhaps
KLAR as well. Winds will turn to the northwest behind a cold front
expected to move across the forecast area later this morning, with
gusts 35-45 kts possible at most terminals this afternoon. Snow
showers will expand eastward to near KAIA and KCDR as the front
moves over these locations. KCYS and KSNY may not see snow due to
dry downslope effect. Winds will ease tonight as the front moves
quickly to the south and east, although will likely remain a bit
breezy across the plains.


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 WYZ110-

     Winter Weather Advisory until 2 PM MST this afternoon for WYZ101.



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