Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171548

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

Issued at 831 AM MST Fri Nov 17 2017

Tricky forecast for late this morning and this afternoon with
relatively light winds across the region so far. Moderate to heavy
snow is falling across the foothills of Carbon and Albany counties
with some accumulation on the roads based on current webcams along
I-80. The big question is winds, currently seeing winds as low as
5 to 10 mph with some locations along I-80, east of Laramie,
around 30 mph. The frontal system has seems to stall across
central Wyoming as a broad surface low has formed across east
central Wyoming. The issue is, the main cold air push is not
forecast to be here until late this evening with rapid pressure
rises behind the front. However, midlevel winds will decrease by
this time. Will give the High Wind Warning a few more hours, but
if winds are not showing signs of increasing, will likely cancel
the warning early. Primary forecast concern this evening will then
become snowfall amounts across southeast Wyoming.


.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

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 12Z TAFS through 12Z Saturday morning)
Issued at 505 AM MST Fri Nov 17 2017

Wyoming TAFS...MVFR at Rawlins until 18Z, then IFR until 01Z, then
VFR. VFR at Laramie until 20Z, then MVFR until 06Z, then VFR. VFR
at Cheyenne until 00Z, then MVFR until 06Z, then VFR. Wind gusts
of 30 to 42 knots.

Nebraska TAFS...VFR at Chadron and Alliance until 01Z, then MVFR
until 06Z, then VFR. VFR at Scottsbluff. VFR at Sidney until 04Z,
then IFR. Wind gusts of 25 to 32 knots late this afternoon and
this evening.


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


WY...Winter Storm Warning until 11 PM MST this evening for WYZ112-114.

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

     High Wind Warning until 2 PM MST this afternoon for WYZ106-



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