Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 252332

Area Forecast Discussion
National Weather Service Cheyenne WY
530 PM MDT Mon Sep 25 2017

.SHORT TERM...(This evening through Wednesday Night)
Issued at 224 PM MDT Mon Sep 25 2017

Tonight...Primary concern is the possibility of frost late tonight
along and east of Interstate 25. Main upper trough aloft is forecast
to move into the Dakotas after midnight with westerly flow aloft
over our counties. Clearing skies expected after midnight, which
should aid in the development of fog formation in the moist, low
level airmass. Still though, based on guidance minimum temperatures,
and coordination with our neighboring offices in Rapid City, North
Platte and Denver, feel it is prudent to issue a Frost Advisory for
late tonight for our counties along and east of Interstate 25. Will
carry low POPS for showers this evening with some instability and
cooler temperatures aloft.

Tuesday...Quite pleasant early Fall day with minimal cloud cover and
a decent warming trend as most lower elevations climb into the 60s.

Tuesday night...May see some increasing clouds in advance of the
approaching upper trough near the Four Corners. Not quite as cold as
the airmass warms and moderates.

Wednesday...Cloud cover continues to slowly increase across our
southern counties in advance of the approaching upper trough near
the Four Corners, which may help to limit the warming trend over
southern counties. Further north, over our northern counties,
temperatures will be warmer than Tuesday, as the airmass continues
to moderate.

Wednesday night...Models indicate the upper trough aloft moving into
western Colorado, with increasing low and mid level moisture over
our counties and a possible shortwave trough aloft passage, aiding
in the development of isolated to scattered showers over our central
and southern counties near the Colorado state line.

.LONG TERM...(Thursday through Monday)
Issued at 224 PM MDT Mon Sep 25 2017

Upper low over Utah early on
Thursday lift NE over Wyoming through Friday while weakening.
Guidance has come into better agreement on a period of rain or
showers lifting northward around this circulation Thursday as upper
diffluence increases and weak warm advection occurs over the plains.
As the upper low departs on Friday attention will shift to a strong
Pacific jet forecast by most of the medium range models to impinge
on the west coast by Saturday.  This will likely lead to a return to
an unsettled weather pattern for the end of the weekend into early
next week with the potential for a couple of quite windy days.


.AVIATION...(For the 00Z TAFS through Tuesday afternoon)

MVFR CIGS will continue east of the Laramie Range early this
evening, but CIGS should lift between 02z-06z. Can not rule out a
thunderstorm near KLAR and KCYS until 03z this evening as a line of
thundershowers has recently developed along the Laramie Range late
this afternoon. With a moist ground and light E to SE winds over the
plains tonight, think low clouds and fog are a good possibility once
again so have included MVFR to IFR conditions returning to many
sites by 06Z. Not very confident about low CIGS and fog at KCYS due
to winds gradually shifting into the west overnight.


Issued at 224 PM MDT Mon Sep 25 2017

No concerns based on projected winds and humidities.


WY...Frost Advisory from 1 AM to 7 AM MDT Tuesday for WYZ101-102-107-

NE...Frost Advisory from 1 AM to 7 AM MDT Tuesday for NEZ002-003-



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