Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 192209 CCA
AFDCYS

Area Forecast Discussion...Corrected Aviation
National Weather Service Cheyenne WY
253 PM MST Sun Feb 19 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 230 PM MST Sun Feb 19 2017

Tonight...Shortwave trough aloft and cold front move from west to
east across our counties. Although gradients not really impressive,
it appears the cold advection combined with GFS progged winds at 700
mb of 50 knots may be enough to produce brief wind gusts near 60 mph
for Bordeaux and the I-80 summit as subsidence takes over. Looks
like a borderline situation for strong winds, though close enough to
warrant possible high winds, so we have upgraded to a high wind
warning.

Baroclinic band passage and cold air advection will produce a chance
of rain and snow this evening, with precipitation mainly north of a
Douglas to Kimball line after midnight.

Washington`s Birthday...Dry and windy day in the wake of the
shortwave trough aloft and with the flow aloft turning zonal. Low
level downslope warming will still produce a mild day, though not as
mild as today.

Monday night...A better chance for high winds near wind prone
locations with stronger low and mid level gradients and progged
Craig to Casper 700/850 mb height gradients.

Tuesday...Continued mild, especially east of Interstate 25 based on
progged thicknesses and 700 mb temperatures. Influx of more low and
mid level moisture will produce a chance of afternoon rain or snow
over far western Carbon County.

.LONG TERM...(Tuesday night through Sunday)
Issued at 245 PM MST Sun Feb 19 2017

The main challenges with the long term will focus on the position
of the cold front, temperatures, winds, instability and large scale
lift for widespread precipitation later this week.

The culprit system that will bring a marked change from springlike
to wintry weather later this week will be moving onshore into the
western CONUS by Wednesday morning. Downstream across our CWA, a
strengthening west to southwest flow aloft will bring increasing
chances for rain and snow along and west of the Laramie Range
Wednesday. It will be breezy across much of the area as well with
gusts of 25 to 35 mph, especially for southeast Wyoming. Wednesday
will be the last mild day of the long term with highs in the 50s
to mid 60s east of the Laramie Range. Precipitation and intensity
will ramp up Wednesday night and Thursday as QG lift increases
across the left front quadrant of a potent upper jet. A strong
cold front will push south across Wyoming and western Nebraska
Thursday. Surface cyclogenesis over southeast Colorado and western
Kansas will increase the northeasterly upslope winds. Frontogenetical
forcing with elevated instability may lead to banded moderate to
heavy snow. Timing of the heaviest snow will be from Wednesday night
through Thursday night. At this time, the mountains and portions
of the northern and eastern plains could receive more significant
snow accumulations. Confidence, however, is low to moderate given
the model uncertainty. The snow will taper off for all but the
southern Wyoming mountains Friday where lingering moisture and
weak orographic lift will persist.

It will turn much colder Wednesday night and Thursday, with below
normal temperatures through Sunday. Brisk northwesterly winds could
drive wind chill values down to advisory criteria both Thursday
and Friday nights for the higher valleys of southeast Wyoming. The
active wintry pattern should continue late next weekend as
another Pacific low pressure system tracks southeast across
California and the Desert Southwest. Precipitation with this
system may encompass much of southeast Wyoming and western
Nebraska Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1016 AM MST Sun Feb 19 2017

Ceilings will lower through the mid afternoon, with MVFR ceilings
developing west of the Laramie Range by this evening with passing
rain/snow showers. VCSH for terminals east of the Laramie Range
after 03Z. The mountains will be obscured this afternoon and
tonight. Westerly winds will become gusty this afternoon across
southeast WY and continue tonight. Gusts of 25 to 40 kt are
expected, highest near the mountains.

&&

.FIRE WEATHER...
Issued at 200 PM MST Sun Feb 19 2017

Minimal concerns based on projected humidities the next several
days.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Monday evening through Tuesday morning for
     WYZ106-110-116-117.

     High Wind Warning from 8 PM this evening to 5 PM MST Monday for
     WYZ106-116-117.

NE...None.
&&

$$

SHORT TERM...RUBIN
LONG TERM...MAJ
AVIATION...MAJ
FIRE WEATHER...RUBIN


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