Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 151138 AAA
AFDCYS

Area Forecast Discussion...UPDATED
National Weather Service Cheyenne WY
538 AM MDT Fri Sep 15 2017

.SHORT TERM...(Today through Saturday night)
Issued at 259 AM MDT Fri Sep 15 2017

Vigorous shortwave seen on GOES 16 WV imagery early this morning
over NW CO will traverse the state of Wyoming this morning. Large
scale upper trough digging into the northern Rockies and Great
Basin will then lift eastward across the area on Saturday.

At the surface, a strong cold front just north of our CWA this
morning will blast quickly southward this afternoon and evening
over the plains and into Colorado tonight. Widespread shower
activity is expected ahead of the above-mentioned shortwave this
morning with a break in the showers expected especially over our
SE`ern counties this afternoon. SW winds are expected to increase
late this morning into early afternoon over Carbon and Albany
counties as the low level gradients tighten and become more
favorably oriented post shortwave. Gusts to 40 mph are likely in
the wind prone areas. As the front crashes south this evening,
showers are expected to break out once again, especially along and
northwest of a Saratoga to Douglas line where the better upper
dynamics will be aligned with the low level frontal zone. Showers
will also spread east of the Laramie Range through Saturday
morning but will be lighter and more scattered in nature after the
front passes as the better forcing for ascent will remain well to
our north and west. Snow levels will drop to around 9000 ft
tonight over our western zones behind the front so rain showers
will change to snow showers for the Sierra Madre and Snowy Ranges.
A quick 2 to 3 inches are likely for the highest elevations before
the precip ends early Friday morning. It will be quite chilly on
Saturday with high temperatures struggling into the upper 50s west
to mid 60s east. Breezy conditions will develop as steep low level
lapse rates and cold advection will mix some higher momentum air
down especially over Carbon and Albany counties. Gusts to 40 mph
will once again be possible during peak mixing in our wind prone
areas.

.LONG TERM...(Sunday through Thursday)
Issued at 259 AM MDT Fri Sep 15 2017

Shortwave lifts out to the northeast early Sunday with some
lingering PoPs east of the Laramie Range, then a dry slot is
expected to work in across the area Monday into Tuesday in the
southwesterly upper flow with clearing skies and drier/warmer
conditions until Tuesday night and Wednesday when another strong
cold front moves in from the northwest dropping temperatures back
again 10 to 15 degrees below readings early in the week. We are
advertising chance PoPs Wednesday west and north with slight
chance east. We may see a few isolated rumbles of thunder
Wednesday afternoon and evening along and east of the Laramie
Range where modest instability will be present. More snow expected
Wednesday night into early Thursday for the higher elevations of
the Snowy and Sierra Madre Ranges, but at this time accumulations
appear to be shaping up to remain below advisory levels.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 538 AM MDT Fri Sep 15 2017

We are getting the expected IFR ceilings across the northern
Nebraska Panhandle with scattered showers and isolated
thunderstorms persisting across southeastern Wyoming and points
eastward on the eastern periphery of an upper low slowly making
progress to the north across central Wyoming. As the low lifts
out, the showers and isolated thunderstorms will gradually weaken
through 16Z. A fairly strong cold front will move south across the
region late today bringing more low ceilings and scattered rains
to most airports 23-03Z.

&&

.FIRE WEATHER...
Issued at 259 AM MDT Fri Sep 15 2017

Cooler weather and precipitation will preclude much in the way of
fire weather threats through the weekend.

&&

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

$$

SHORT TERM...DEL
LONG TERM...JG
AVIATION...JG
FIRE WEATHER...DEL



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