Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 210545

Area Forecast Discussion
National Weather Service Cheyenne WY
1145 PM MDT Thu Apr 20 2017

Issued at 1137 PM MDT Thu Apr 20 2017

Latest guidance indicates the potential for heavier banded precip
over the Laramie Valley and the South Laramie Range early this
morning as an area of mid level deformation and low level
frontogenesis sets up over SE WY. NAM and GFS forecast soundings
indicate deep saturation through the dendritic zone through about
15 to 18z with snow levels lowering to 6500 ft. Negative EPV
values co-located with intense low level frontogenesis lend
credence to the idea of banded precip so have upgraded the Laramie
Valley to an advisory. There is concern also that snow amounts for
the South Laramie Range might be too low will need to monitor
latest radar/satellite trends through the over night hours for
possible upgrade. Increase snow totals a bit east of the Laramie
Range into the Cheyenne area as heavy precip rates will drive snow
levels to the surface early Friday morning. 1 to 2 inches of
slushy accumulation look likely but road surfaces should remain


.SHORT TERM...(Tonight through Saturday)
Issued at 223 PM MDT Thu Apr 20 2017

Clouds increasing over the CWA this afternoon with showers also
increasing gradually over and near the higher mtns. This in
response to digging upper shortwave now over the Pacific
northwest. This system will continue to drop southeast overnight
and close off an upper low over Colorado during the day Friday.
Rains and higher elevation snow will increase across mainly the
southwest half of the CWA overnight and continue across most of
the CWA Friday before tapering off Friday night. Main difficulty
will continue to be the level of accumulating snow later tonight
into Friday. Still appears that will be generally above about
7000 feet so current Winter Wx Advy looks good overall though the
start of the snow over the South Laramie Range may hold off until
later this evening. Some snow likely to fall as well later tonight
into Friday morning down to around 6000 feet or so but initial warm
ground and Sun angle likely to limit accumulations late tonight
and Friday. Winds modest and should not create much of a problem.
Much cooler over much of the CWA Friday given clouds and pcpn with
chilly conditions Friday night. System pulls away Friday night
and saturday allowing for warmer weather to begin its return on

.LONG TERM...(Saturday night through Thursday)
Issued at 223 PM MDT Thu Apr 20 2017

A warm and dry start to the extended forecast period w/broad upper
level ridging in place. Strong subsidence beneath the ridge should
preclude any risk for precipitation through Sunday evening. Expect
highs in the 60s and 70s with H7 temperatures of +5 to +7 C. GFS &
ECMWF both suggest a fast moving short-wave trough tracking across
the central Rockies on Sunday night/Monday. Jet energy is expected
to be fairly modest, but 700-300 hpa RH progs show sufficient mid/
high level moisture for scattered precipitation coverage. It looks
like the overall pattern will remain rather unsettled through much
of next week with numerous waves embedded w/in fast WNW flow aloft
through Thursday. Medium range models suggest a deepening low over
the western US mid to late week, which could have the potential to
bring widespread precipitation to the CWA.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1109 PM MDT Thu Apr 20 2017

LIFR to IFR ceilings and visibility tonight into Friday morning
for Cheyenne and Laramie where stronger dynamic forcing for
precipitation is expected overnight through mid morning, with IFR
to MVFR visibilities Rawlins 12z-16Z in snow showers. Farther east
onto the plains rain is slowly making its way eastward across the
southern Panhandle with IFR ceilings and visibility expected at
Sidney by 10Z, and MVFR ceilings expected for Alliance,
Scottsbluff and Chadron by 12Z.


Issued at 223 PM MDT Thu Apr 20 2017

Wetting pcpn expected across much of the area tonight and Friday
with cooler temperatures. This will keep fire weather concerns nil
through at least the weekend.


WY...Winter Weather Advisory until 6 PM MDT Friday for WYZ112-114-116.

     Winter Weather Advisory until 3 PM MDT Friday for WYZ115.



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