Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 072056
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
156 PM MST Thu Dec 7 2017

.SHORT TERM...(Tonight - Saturday)
Issued at 124 PM MST Thu Dec 7 2017

Light snow showers will linger through this afternoon, mainly over
southeast Wyoming. Overall impacts from this activity will be low,
but heavier showers could create slick roads and low visibility in
some areas. Any accumulations will be less than an inch, except in
the Snowy and Sierra Madre mountains where several inches may fall
through tonight. Mid-level energy is expected to move southeast of
the area by 00z, effectively ending precipitation chances for some
time to come.

High wind concerns for tonight and Friday. A significant upper-lvl
jet will set up over the central Dakotas, placing much of the high
plains in the RFQ of a 120+ knot H25 jet streak. The models are in
good agreement with H7-H8 flow of 55-65 kts along/E of the Laramie
Range between 06z and 12z, and an impressive W-E pressure gradient
along the spine of the Laramie Range. This, combined w/significant
subsidence may yield 50+ knot gusts over the I80 summit, and maybe
even Bordeaux as well despite northwest flow typically being an un
favorable pattern. We opted against High Wind Warning issuance for
the time being based on the pattern, and the fact that the HRRR is
only showing around 40 knot gusts through 12z. The latest forecast
soundings from the GFS also show enough of an inversion to support
the restriction of downward momentum transfer. Later shifts should
monitor this closely, however.

The GFS shows H7-H8 flow remaining in the 50-55 knot range through
mid/late Friday afternoon. This could become a concern with clouds
diminishing and improved low-level mixing after 18z. We anticipate
much of the high plains to be very close to warning-level winds on
Friday afternoon, w/ mixing and subsidence likely supporting 50-55
MPH gusts for all areas along/e of the Laramie Range. The question
mark right now is mixing depth, so confidence right now is too low
to warrant High Wind Watch/Warning issuance. We would also like to
see higher numbers on MAV/MET guidance for any highlights.

.LONG TERM...(Saturday Night - Wednesday)
Issued at 210 AM MST Thu Dec 7 2017

Weather dominated by ridge of high pressure to the west. We stay
in northwest flow. Clipper systems look to stay east of Wyoming
and western Nebraska. Dry forecast expected through Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1035 AM MST Thu Dec 7 2017

Wyoming TAFS...VFR, except for periods of MVFR at Laramie from 18Z
to 22z. Wind gusts to 37 knots through 02Z. Wind gusts to 35 knots
again after 08Z.

Nebraska TAFS...VFR. Wind gusts to 32 knots through 00Z. Wind
gusts to 35 knots again after 06Z.


&&

.FIRE WEATHER...
Issued at 210 AM MST Thu Dec 7 2017

Breezy to windy conditions will persist mainly east of the mtns
today through Friday with a bit less wind on Saturday. Min
humidities well above critical thresholds today then they do get
down to around 20 percent across far se Wy into the southern Neb
Panhandle both Friday and Saturday so a bit of an elevated
concern there.

&&

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

$$

SHORT TERM...CLH
LONG TERM...GCC
AVIATION...RUBIN
FIRE WEATHER...RE


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