Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171821
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1121 AM MST Fri Nov 17 2017

.UPDATE...
Issued at 937 AM MST Fri Nov 17 2017

Decided to cancel the High Wind Warning through early this
afternoon. Current observation are showing evidence of a surface
low north of I-80 with a warm front extending southeast across the
High Plains of southeast Wyoming with winds actually more out of
the east, east of I-25. The surface low is broad with no clear
sign of circulation. In Cheyenne, winds have been variable through
most of the morning but have shown signs of shifting into the
northeast at times. Focus will then shift westward through this
afternoon as snow is picking up in intensity and snowlevels are
lowering along and west of the Laramie Range. May need to extend
current advisories into the lower elevations since rain has
changed to snow a little earlier than expected.

&&

.SHORT TERM...(Today through Saturday night)
Issued at 307 AM MST Fri Nov 17 2017

Complicated forecast in the short term for today through tonight
as a strong cold front approaches the area from the northwest.

Currently...Cold front lays along a line from central South
Dakota to Newcastle to Riverton to near Evanston this morning. So
far, precip has stayed west and north of our CWFA, but it really
is getting close. Just about to come into western Converse and
Carbon Counties. Winds are really cranking at Bordeaux already
this morning with 68mph reported so far as the peak gust. In an
earlier update, did add Bordeaux into a High Wind Warning along
with the area previously Watched for the south Laramie Range and
most of Laramie County.

Due to slower movement of the front, thinking here is that precip
will take a little longer to get through the mountains. So went
ahead and extended the Winter Storm Warnings again til late
tonight instead of this afternoon. Also added the Arlington area
into a Winter Weather Advisory for snow and blowing snow. Precip
should come to an end pretty quickly after midnight tonight.

Bora wind event still looks on track for most of Laramie County
and the South Laramie Range. NAM 750mb winds doing a pretty good
job as it picked up the Bordeaux event this morning. Strong winds
drop south to Cheyenne and the Summit after 12Z and then really
begin to drop off after 18Z. Day shift will need to determine wind
trends and either cancel/extend depending on these trends.

.LONG TERM...(Sunday through Thursday)
Issued at 307 AM MST Fri Nov 17 2017

Sunday...A decent warming trend begins as the flow aloft backs to
almost straight westerly with a surface lee trough forming. With a
bone dry airmass, no precipitation is anticipated. Will stick close
to guidance maximum temperatures.

Monday...Fast moving shortwave trough aloft approaches from southern
Idaho in the afternoon with strong zonal flow aloft helping to
produce a windy day. Continued mild like Sunday based on thicknesses
and 700 mb temperatures. By early evening, chances for showers will
spread across Carbon County in the moist orographic flow aloft.

Tuesday...Fast moving shortwave trough aloft moves southeast into
Colorado by dawn, with fast northwest flow aloft across our counties
in the afternoon. Drying out in the afternoon behind the shortwave
trough aloft and breezy to windy per progged surface to 700 mb
gradients.

Wednesday...Another warming trend begins with rising heights and
thicknesses on northwest flow aloft. Flow at the surface and aloft
remains strong enough for windy conditions, and possible high wind
criteria across our wind prone locations.

Thanksgiving...Mild temperatures continue as the flow aloft backs to
westerly with relatively high heights aloft...5780 meters at 500 mb,
along with downslope warming. Low and mid level moisture look too
scant for any precipitation.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1057 AM MST Fri Nov 17 2017

The main concern with this TAF issuance is the wind direction at
the Wyoming TAF sites today. Latest surface analysis is showing
that the models are struggling with the surface pressure fields.
As a result, we are seeing the models struggling with the wind
fields. Based on the latest surface analysis, we would anticipate
a later cold frontal passage. It looks like frontal boundary
should pass through this evening with some shortlived post
frontal precip. following behind it.

&&

.FIRE WEATHER...
Issued at 345 AM MST Fri Nov 17 2017

Strong cold front approaching from the west and northwest this
morning will keep strong winds going today. This front will also
bring heavy mountain snow and a mix of rain/snow to valley floors
west of the Laramie Range before turning all snow this afternoon.
Temperatures will be decreasing behind the front, so afternoon
humidities should stay well above critical levels. An extended
windy pattern over the next several days with afternoon humidities
east of the Laramie Range getting close to critical Sunday and
Monday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Warning until 11 PM MST this evening for WYZ112-114.

     Winter Weather Advisory until 11 PM MST this evening for WYZ110.

NE...None.
&&

$$

UPDATE...TJT
SHORT TERM...GCC
LONG TERM...RUBIN
AVIATION...REC
FIRE WEATHER...GCC



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