Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 190945

Area Forecast Discussion
National Weather Service Cheyenne WY
345 AM MDT Thu Oct 19 2017

.SHORT TERM...(Today through Friday night)
Issued at 230 AM MDT Thu Oct 19 2017

Main concerns this period will be focused on Fire Weather given
the continuation of the dry and unseasonably warm conditions and
some gusty winds through Friday afternoon. Strongest winds will be
over western and northern parts of the CWA this afternoon as the
upper flow becomes southwesterly. Quite windy over western areas
on Friday as 700H winds increase to about 45 kts ahead of an upper
trough that will move over the Pacific Northwest during the day
before swinging across the northern and central Rockys Friday
night. At the same time, a strong cold front will sweep east across
the CWA Friday evening with some potential for a Bora type wind
event behind the front as 700H winds exceed 50 kts for a time
around the South Laramie Range. Not much pcpn expected with the
front outside of some rain to snow showers primarily over the
Snowy/Sierra Madre Ranges Friday evening. A few inches of snow
possible over the higher peaks there.

.LONG TERM...(Saturday through Wednesday)
Issued at 345 AM MDT Thu Oct 19 2017

Primary forecast concern will be high wind potential Saturday
night through Monday morning for southeast WY.

Deep upper trough will advance eastward from the Rockies into
the Great Plains through Saturday night. Shower activity over
the mountains will end by midday. It will be breezy and colder
Saturday with west-northwest winds gusting to 40 mph from the
southern Laramie Range east along the I-80 corridor. High
temperatures will be in the 40s and 50s, with 20s and 30s over
the mountains.

Strong west-northwest flow aloft will prevail Saturday night through
Monday as a series of shortwaves move west to east from the Pacific
Northwest across the northern Rockies and Plains. 700mb winds
increase to 55 kt over the wind corridors of southeast WY, with
Craig-Casper 700-850mb height gradients of 60-75m between 03Z
Sunday and 18Z Monday. Models have been consistently targeting
this time period for high winds, and high wind headlines will need
to be considered as we draw closer to the event. While the wind
prone areas like Arlington, Bordeaux and the southern Laramie
Range/foothills are favored, cannot rule out the possibility of
strong winds spreading out onto the eastern WY plains Sunday
night/Monday morning. After a cool Saturday, downsloping winds lee
of the Laramie Range will quickly moderate temperatures to above
seasonal normals Sunday/Monday.

Another reinforcing cold front will cool temperatures to seasonal
normals Tuesday, followed by a 5-10 degree warmup Wednesday as a
upper ridge takes dominates the Intermountain West.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 215 AM MDT Thu Oct 19 2017

VFR. South to southwest winds 10-15 kt become breezy this afternoon,
gusting to around 25 kt at Rawlins, as well as Alliance and Sidney.
Winds will diminish to 8-15 kt this evening.


Issued at 215 AM MDT Thu Oct 19 2017

It will be breezy over western and northern districts again this
afternoon and with dry fuels over northern areas will keep the Red
Flag Warning up in that area, as well as for the upper North Platte
River basin. It appears winds over the South Laramie Range will
remain low enough to limit concerns so have opted to cancel the
Red Flag Warming there. Min RHs should be a little higher on Friday
but will have to watch as more widespread gusty winds should occur
ahead of a strong cold front that will sweep across the area Friday
evening. Breezy to windy and much cooler Saturday.


WY...Red Flag Warning from 11 AM this morning to 6 PM MDT this
     evening for WYZ301-306.



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