Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 210909

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

Issued at 205 AM MST Tue Nov 21 2017

Radar and satellite along with short term model trends continue to
indicate a persistent band of snowfall training along the Snowy
Range early this morning. This banding is noted downstream from an
intense 170 kt upper jet and this is probably contributing some
inertial instability due to fast flow over the high terrain to the
northwest. This should continue through the early morning hours
before the jet begins to weaken and shift south. Snowfall could be
locally heavy right along the spine of the Snowy Range with local
totals of up to 9 inches possible. Issued a Winter Weather
Advisory to account for these trends through 11 am.

UPDATE Issued at 1043 PM MST Mon Nov 20 2017

Sending out another quick update to keep the high wind warning
going until 3am, due to strong wind speeds persisting. Would
expect Bordeaux wind speeds to drop off sooner than the southern
Laramie range as the front approaches from the north.

UPDATE Issued at 739 PM MST Mon Nov 20 2017

We are sending out a quick update to extend the high wind warning
through 11pm. Latest satellite loop was showing some mountain wave
activity taking place around Bordeaux. This mountain wave activity
may persist during the next few hours or so as a mid level
shortwave progresses through the area. Latest observations were
also still showing wind speeds around 50 to 60 in parts at Strouss
hills which is about 10 miles northeast of Centennial and still
some 50 mph along the foothills of the Laramie Range. We are also
are also considering on bumping up snowfall amounts tonight in the
snowy range along with inserting some snowfall near the I-80
summit late tonight due to good upslope flow and some good
moisture advection for a few hours towards daybreak.

UPDATE Issued at 505 PM MST Mon Nov 20 2017

We sent a quick update to let the High Wind Warning expire for
portions of Southeast Wyoming. Wind speeds have subsided for now,
but they pickup again later this evening as a weak shortwave
passes through the area.


.SHORT TERM...(This evening through Tuesday night)
Issued at 232 PM MST Mon Nov 20 2017

Strong winds gradually dropping off now as the gradient is
lessening. Expect this trend to continue for the rest of the
afternoon thus it appears the current hilites will be allowed to
expire as planned though may have to watch around the S Laramie
Range as 7H winds still progged around 60 kts through this
evening. Otherwise fairly large area of high clouds will move
across the CWA overnight with some snow showers increasing over
the mtns as this increased moisture rides up the nw facing slopes.
Should see about 3-6 inches over the higher peaks later tonight
into Tuesday morning before it tapers off. More isolated rain and
snow showers possible over the plains. Much cooler east of the
mtns Tuesday as the front backs up against the mtns. The front
should begin to retreat back east Tuesday night as lee troughing
develops over the high plains.

.LONG TERM...(Wednesday through Monday)
Issued at 232 PM MST Mon Nov 20 2017

Weds through Friday looking dry and unseasonably warm across the
area as upper ridging builds over the western CONUS Weds and
Thursday. Max temps in the 60s to even around 70 over the lower
elevations Weds through Friday. A shortwave will pass across the
region Friday and push a cool front by, bringing a little cooler
air for Saturday. Warming again Sunday and Monday as upper ridging
builds again out west and moves east over the area. Mainly dry
through the period as well.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1031 PM MST Mon Nov 20 2017

Strong wind speeds will persist across the KCYS and KRWL taf sites
through early tonight, before a frontal boundary starts to
approach the area towards daybreak. Before this front approaches
the Laramie Range, we will see the potential for moist upslope
flow which will may bring some snowfall to our higher elevations.
Not expecting much in the way of accumulation at KCYS and KLAR due
to these sites experiencing more downslope flow which will allow
for more drying. Although, cannot rule out some MVFR ceilings
towards daybreak. Meanwhile, the Nebraska TAF sites may also
experience some MVFR ceilings after the front passes through which
should begin to clear out around midday Tuesday. KCDR may also
experience some brief snowfall after the front passes through
around 12z.


Issued at 232 PM MST Mon Nov 20 2017

Fire weather concerns will drop off this evening as gusty winds
ease and humidities recover sufficiently.  A cold front will move
south across the plains later tonight bringing cooler air and
less wind. Fire weather concern quite low for the next few days
with just some breezy areas mainly around the mtns at times but
non-critical humidities.


WY...Winter Weather Advisory until 11 AM MST this morning for WYZ114.

     High Wind Warning until 3 AM MST early this morning for WYZ106-



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