Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 172359
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
559 PM MDT Sun Sep 17 2017

.SHORT TERM...(This evening through Tuesday night)
Issued at 242 PM MDT Sun Sep 17 2017

Early afternoon water vapor loop showed the upper trough axis
entering western WY and northern UT. Scattered convection was
developing across south-central and southeast WY. This trend will
continue, with shower and thunderstorm activity spreading east
into the western Nebraska Panhandle through late afternoon.

Scattered showers and thunderstorms will taper off from west to
east later this evening across the plains as the upper trough
moves through the CWA. A surface ridge of high pressure extending
north into southern WY will prevail Monday with dry and warm
conditions. Expect high temperatures in the 70s to mid 80s.
Southwest winds will be breezy along and west of the Laramie
Range during the afternoon.

Shortwave energy diving southeast from the Gulf of AK into the
Pacific Northwest Monday night will shift east across the northern
Rockies Tuesday. A strong Pacific cold front will race east across
WY Tuesday afternoon and western NE Tuesday night. Scattered
showers will accompany the front, along with cooler temperatures
for portions of south-central southeast WY. 700mb winds increase
to 40-50 kt along and west of the Laramie Range Tuesday, with
westerly surface gusts of 40-45 kt possible. Winds slowly ease
Tuesday night after the frontal passage.

.LONG TERM...(Wednesday through Sunday)
Issued at 242 PM MDT Sun Sep 17 2017

It will be a little cooler Weds in the wake of a Pacific cool
front. Looking breezy to windy as well as favorable southwesterly
upper flow sets up over the region ahead of a digging upper trough
over the Pacific northwest. This system will continue to amplify
Thursday while moving very little, maintaining warm and dry
weather for the CWA given the swly flow aloft. Cooler conditions
should arrive Friday as lee cyclogenesis occurs over Colorado with
the latest EC a little slower than the GFS. Showers should spread
gradually east across southeast Wy Friday with a cool and rather
wet weekend as colder air filters down the high plains under
s-swly flow aloft.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 539 PM MDT Sun Sep 17 2017

Latest radar loop was showing the cluster of showers and
thunderstorms stretching from 30 miles northeast of CYS to BFF.
This cluster of showers and thunderstorms has been slowly building
southeast. Most of the convection should begin to exit the region
by around midnight as the upper level jet and mid level trof departs
the area. Behind this trof, the wind will turn to the west in
Wyoming. May have to watch for the potential for low stratus to
develop where the rain occurs late this evening. May have to
amend TAF`s around BFF and AIA, but we will look at future model
runs to help us weigh in on this potential. The remainder of the
TAF sites is expected to be in the VFR category.


&&

.FIRE WEATHER...
Issued at 245 PM MDT Sun Sep 17 2017

Upper level trough will shift east across the districts this
afternoon and evening with scattered showers and thunderstorms.
Drier, breezy and warmer conditions return Monday ahead of a
strong Pacific trough and cold front. Westerly winds increase
Tuesday with the frontal passage, along with scattered showers and
cooler temperatures. Mild and dry conditions Wednesday and
Thursday will be replaced by much cooler and wetter weather
Friday through next weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

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



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