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000
FXUS65 KCYS 181217 CCA
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
517 AM MST Mon Feb 18 2019

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM MST Mon Feb 18 2019

Broad long wave trough extended from the Upper Midwest through the
Great Plains and Intermountain West. Several pieces of energy continue
rotating through base of the trough and ejecting northeast. A potent
short wave was lifting northeast into southern UT, with numerous
snow showers spreading through CO. The northern edge of the showers
was along the I-70 and I-76 corridors. Some of this activity will
spread north to the CO/WY border early this morning. The other
story is the very cold temperatures, with wind chills from -10 to
-25 degrees. Wind Chill Advisories are in effect until 9 AM from
east central WY into northwest and central NE.

Forecast concerns will focus on cold temperatures, PoPs, snow amounts,
and potential for stronger winds across portions of southeast WY on
Wednesday.

Snow showers will become more prevalent along and south of I-80
corridor today, spreading north and east tonight and Tuesday as
surface low moves across south central CO. Increasing upslope and
QG lift will enhance snow accumulations, especially the high
terrain and plains near the CO border where 2 to 3 inches may
fall. It will remain unseasonably cold today through Tuesday night
with 700mb temperatures from -16 to -20C. Highs today will be in
the teens outside the mountains, and in the teens to around 20
Tuesday. Cloud cover and lighter winds tonight and Tuesday morning
will keep wind chills in check, mainly -5 to -15 degrees. Wind
chills western valleys and high terrain Tuesday night will approach
-20 degrees with increasing winds. This seqways into the next
potential high wind episode late Tuesday night and Wednesday with
the passage of a short wave trough. Models have been consistent the
past three days, with CAG-BRX 850mb gradients peaking above 60mtrs
and Bordeaux high wind probabilities of 50-60 percent. NAM/GFS 700mb
winds rise to around 50kt between 12Z and 18Z over the
central/southern Laramie Range and north Snowy Range foothills.
Bordeaux and to a lesser degree, Arlington, may be affected by these
gap winds. If model trends continue, High Wind headlines may be
issued as early as Tuesday morning. Downslope flow will moderate
temperatures Wednesday into the 20s to low 30s east of the Laramie
Range.

.LONG TERM...(Wednesday night through Sunday)
Issued at 245 AM MST Mon Feb 18 2019

Medium range models/ensembles maintain the broad long wave trough
as migratory shortwaves anchor it over the western 2/3 of the
CONUS. The most active period of snow showers will be Thursday
through Friday as a closed low over the Great Basin opens and
progresses eastward across the Rockies and a Canadian front slips
south into the CWA. After the passage of the trough Saturday
morning, a faster zonal flow develops, with windy conditions for
much of southeast Wyoming. Below normal temperatures will prevail
through the long term, with highs moderating into the 30s east of
the Laramie Range this weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 517 AM MST mon Feb 18 2019

Sctd MVFR/IFR cigs early this morning should give way to mainly
VFR this afternoon into this evening before becoming mostly MVFR
again later this evening and overnight.  A few snow showers around
as well during the period with light surface winds.

&&

.FIRE WEATHER...
Issued at 215 AM MST Mon Feb 18 2019

Fire weather concerns will be low this week with colder than normal
temperatures and periodic chances for snow showers. Minimum relative
humidities each day will be above critical levels. It will be windy
throughout the southeast Wyoming districts Wednesday and again this
weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Wind Chill Advisory until 9 AM MST this morning for WYZ101-102.

NE...Wind Chill Advisory until 9 AM MST this morning for NEZ002-003-
     095.

&&

$$

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