Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 172331
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 PM MDT Tue Oct 17 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 134 PM MDT Tue Oct 17 2017

Weak shortwave over western Nebraska early this afternoon will
exit the region to the east early this evening. More shortwave
energy trailing south from a strong disturbance over the Pacific
Northwest will cross Southeast Wyoming late tonight.

Currently, deep mixing and subsidence in the wake of the first
disturbance has led to the development of widespread critical fire
weather conditions this afternoon. RH values have fallen as low as 7
percent and winds are gusting between 30 and 40 mph over Wyoming and
20 to 30 mph in western Nebraska.

As the second piece of energy moves over head tonight, low level
gradients will tighten.  CAG-CPR gradients between 06 and 12z
tonight peak around 45m so kept winds up in our more wind prone
locations over night where gusts between 40 and 50 mph are likely.

Weak ridging builds overhead on Wednesday.  It should be a warm,
very dry, and generally less breezy day as the fastest mid level
flow shifts north of our area and a weak surface high/cool front
backs into the plains.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 134 PM MDT Tue Oct 17 2017

Winds are the story in the long term. Confidence increasing on a
fairly widespread high wind event that may come at two different
times. First being Friday late afternoon through Saturday morning
as an upper level shortwave moves through the area. 700mb winds
increase to 55-60kts across southeast Wyoming while GFS Craig to
Casper 850/700mb height gradients top out in the low 70mtr range.
This event may be confined to the wind prone areas (Arlington,
Bordeaux, south Laramie Range).

Fairly windy Saturday through the day. Winds may stay just below
high wind criteria for the day, but Craig to casper 850/700mb
gradients again increase Saturday night and persist through most
of Sunday into Monday. GFS guidance showing gradients peaking out
at 78/74mtrs respectively by 12Z Monday. This event looks to be
more widespread and we could be looking at warning level winds
here in Cheyenne, Laramie, Rawlins and possibly Wheatland. Will
continue to monitor, but did start increasing winds over guidance
for these timeframes.

&&

.AVIATION...(For the 00Z TAFS through Wednesday afternoon)

VFR conditions expected over the next 24 hours with intervals of
high clouds moving through the region. Gusty winds this evening will
become lighter overnight.  Winds should not be as strong on
Wednesday but gusts around 25 knots are possible from KCYS westward
into the KRWL area.

&&

.FIRE WEATHER...
Issued at 134 PM MDT Tue Oct 17 2017

Very dry airmass in place this afternoon with critical fire
weather conditions occurring in all locations where fuels are
receptive with the exception of the far northern Panhandle. Very
dry conditions will continue on Wednesday, however the strongest
winds at low to mid levels will shift north. There will likely be
just enough wind at peak mixing for the S. Laramie Range to hit
critical conditions for a few hours Wednesday afternoon so issued
a Fire Weather Watch for zone 309. Elsewhere, elevated conditions
will occur across the rest of Southeast Wyoming especially Carbon
County where the fuel status is currently not favorable.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...Fire Weather Watch Wednesday afternoon for WYZ309.

NE...NONE.

&&

$$

SHORT TERM...DEL
LONG TERM...GCC
AVIATION...TJT
FIRE WEATHER...DEL



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