Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 132333

Area Forecast Discussion
National Weather Service Cheyenne WY
308 PM MST Mon Nov 13 2017

.SHORT TERM...(Tonight - Wednesday)
Issued at 232 PM MST Mon Nov 13 2017

No significant weather impacts are expected over the next 24 to 48
hours across southeast WY and the western NE Panhandle. A very dry
air mass remains in place, as evidenced by only thin cirrus clouds
seen on afternoon Visible Satellite imagery. Breezy conditions are
expected to develop in the wind corridors during the overnight hrs
as weak pressure falls spread across the high plains of eastern MT
and northeast WY. The NAM/GFS both show H7 CAG-CPR gradients of 30
to 40 meters, with H7-H8 flow around 30 to 40 knots. The low-level
gradients will increase further on Tuesday, rising to between 40 &
50 meters as a fast-moving shortwave tracks across eastern MT into
northeast WY and the western Dakotas. Subsidence in the right exit
region of a 120 knot 250 mb jet, along w/ strong low-lvl mixing in
the afternoon will further support wind gusts of 40 to 50 MPH over
the wind corridors on Tuesday afternoon. A couple of warning-level
gusts cannot be ruled out at ARL, but the main limiting factor for
a true high wind episode will be the northern track of the surface
low, well to the north of the Canadian border.

Tuesday will be another very warm day with H7 temperatures between
+2 and +4 deg C across much of the CWA, except far northwest where
a cold front will make an earlier arrival. A weak/dry fropa should
occur Tuesday evening/overnight. Highs Wednesday will be 10-15 deg
cooler than Tuesday, but with considerably less wind.

.LONG TERM...(Wednesday night through Sunday)
Issued at 407 AM MST Mon Nov 13 2017

Late-week fast moving compact short-wave trough will be the
culprit to a windy, unsettled, and colder end to the workweek.
Pre-frontal air mass will yield one more mild, but breezy-windy
for Thursday. Highs will climb into the 50s west in Carbon/Albany
counties, with 60s likely on the eastern plains. Winds will be on
the increase, especially west of I-25 Thursday afternoon. Low-
level Craig-Casper gradients of 50-55 meters suggest gust speeds
may approach high wind criteria. Both the GFS/ECMWF show precip
developing in the mountains Thursday afternoon/evening as the
upper-jet outruns the arrival of the cold front. Snow-levels
remain high initially, around 9000 feet late Thursday. Sharp cold
front pushes through Thursday night per the GFS OR Friday morning
per the ECMWF. Either way, precipitation will increase in
coverage and intensity Thursday night and continue through around
midday Friday before ending. It looks to be mainly a mountain
snow event, which will likely see 6+ inches. Lower elevations will
see lighter amounts, however with strong post-frontal wind speeds
producing blowing/drifting snow, travel impacts may be high
despite relatively light snow amounts. The eastern plains should
even see a shot of light snow Friday morning, though the fast-
moving nature of the system will limit anything above an inch or
two. The other concern will be the possibility of another period
of high winds associated with the post-frontal bora. 6-hourly
pressure rises of 7-10mb bullseye parts of SE Wyoming on Friday.
Early MOS guidance also points to the high wind potential Friday.
Much colder air mass for Friday with highs in the 30s west and 40s
east. Seasonal, dry, and breezy to windy conditions to continue
into next weekend.


.AVIATION...(For the 00Z TAFS through Tuesday)
Issued at 1038 AM MST Mon Nov 13 2017

VFR conditions to prevail tonight and Tuesday morning with
intervals of high clouds. Windy conditions are expected by late
Tuesday morning through Tuesday afternoon, especially along and west
of Interstate 25, where gusts up to 40 knots are possible


Issued at 330 AM MST Mon Nov 13 2017

RH values have fallen to around 15 percent across much of the area
this afternoon, but wind speeds are generally below 20 MPH so fire
weather concerns are low overall. Elevated fire weather conditions
are likely on Tuesday, with RH values falling to near 20 percent &
westerly winds of 20-30 MPH with gusts of 40-50 MPH.




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