Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211731
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1030 AM MST Tue Nov 21 2017

.SHORT TERM...(Today and tonight)
Issued at 243 AM MST Tue Nov 21 2017

Upper level shortwave over southern MT will drop south across the
area through this morning. Associated 170kt NW`ly upper jet will
continue to provide some instability for banded snowfall along the
mountains (especially the Snowy`s) through this morning so kept
the Winter Weather Advisory in place. HRRR and other short range
guidance indicates a band of snow developing and tracking over the
South Laramie Range early this morning and this may be happening
based on trends from the Riverton radar. Surface and road temps
are fairly warm and any snowfall should be brief so not expecting
any major travel issues at this time, however trends will need to
be monitored in case there is a training band or the snow is heavy
enough to accumulate in spite of marginal temps.

Elsewhere, a surface cold front is currently moving south through
the plains with a band of light snowfall just behind it over the
extreme northern panhandle. Not expecting much in the way of
accumulation as temps are still above freezing and the ground is
warm. Clouds will increase over the remainder of the plains behind
the front this morning and slowly thin this afternoon. It will be
much cooler and less windy across many areas today.

Upper ridging will build over the intermountain west tonight with
increasingly subsident and anticyclonic flow increasing over SE
Wyoming late tonight. Surface lee troughing will redevelop with H7
flow increasing to 50kt over the S Laramie Range. Low level CAG-
CPR gradients increase to 58-64 meters by 12z Wed. With the mid
and low level flow being more WNW`ly think this is a set up that
favors Bordeaux and the S Laramie Range more than Arlington so
issued a High Wind Watch for these areas. Forecast soundings
indicate mtn wave potential with a decent inversion setting up
around ridge top level along with reverse shear w/height. While a
less sustained and more gusty event than this past one appears
likely, still think there`s the possibility for a few high wind
gusts late tonight.

.LONG TERM...(Wednesday through Monday)
Issued at 243 AM MST Tue Nov 21 2017

Winds are expected to be quite strong early on Wednesday AM across
the primary wind corridors of southeast Wyoming. Otherwise, do not
have any major weather concerns through mid-week as high-amplitude
upper level ridging develops over the western US. Wed & Thu should
be quite warm with the models showing 700 mb temperatures of +4 to
+6 deg C. Large scale ridging will quickly break down later in the
week. The GFS/ECMWF differ considerably in the timing, but both do
agree in a return to strong west-northwest flow aloft over the CWA
by Friday AM as a vigorous mid-level disturbance tracks rapidly to
the east across the northern high plains. As such, breezy to windy
conditions will return to much of the area by Thursday or Friday.

&&

.AVIATION...(For the 18Z TAFS through Wednesday morning)

Remnant MVFR CIGS will quickly lift and disipate by noon today with
FEW-SCT coverage of clouds between 5k to 10k feet AGL. It will be
breezy this afternoon across the southeast Wyoming terminals with
gusts occasionally around 30 KTS.  Winds will be light and variable
across western Nebraska with VFR conditions expected after 19z.

&&

.FIRE WEATHER...
Issued at 243 AM MST Tue Nov 21 2017

Temperatures will be cooler and winds will be less today across
much of the area. Dry, warmer, and breezier weather return for mid
week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Watch from late tonight through Wednesday morning for
     WYZ106-116-117.

NE...None.
&&

$$

UPDATE...DEL
SHORT TERM...DEL
LONG TERM...CLH
AVIATION...TJT
FIRE WEATHER...DEL


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