Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 252110

Area Forecast Discussion
National Weather Service Cheyenne WY
310 PM MDT Tue Apr 25 2017

.SHORT TERM...(This Evening through Thursday)
Issued at 320 PM MDT Tue Apr 25 2017

Current LAPS surface analysis shows a cold front sliding southward
into Colorado this afternoon with a band of convection just along
the boundary. Convection has mainly been a mix of rain, snow
pellets, and grauple further to the west; with thunderstorms and
small hail further to the east. Have had a few reports of funnel
clouds near and east of the Nebraska/Wyoming border with these
cells due to some strong llvl wind shear around 20 to 30 knots
just off the surface, but these funnel clouds have been short-
lived so far. Further north, some snow has been reported, but
snowfall has not impacted the roadways much today as it has melted
after hitting the pavement. This activity will continue over the
next 3 to 5 hours before rapidly dissipating late this evening.
Snowfall may linger across east central Wyoming to the northern NE
panhandle until midnight before tapering off. Little to no
snow accumulation is expected outside the mountains.

Somewhat drier air will move into the area for Wednesday briefly
as a weak shortwave ridge axis quickly moves southeast across
eastern Wyoming. Temperatures will not rebound all that much as
another round of convection is expected in the afternoon once the
ridge axis moves into the plains. Highs will struggle to climb
into the mid 50`s across most of the area, warmest across the
southern NE panhandle. Expect rain/snow showers to develop across
southeast Wyoming and move eastward through the evening. Do not
anticipate any thunder at this time, but can not completely rule
it out either, since model soundings are marginal. Models indicate
the next Pacific disturbance digging southeast into western
Wyoming, so evening convection may continue through most of the
night with the precip type gradually changing to snow.

The beginning of an extended period of chilly unsettled weather
may begin on Thursday as the main Pacific disturbance digs
southeast into the northern intermountain west. Models show the
initial shortwave over southeast Wyoming during the day with
widespread light rain and snow. The GFS shows the wave attempting
to close-off from the mean flow during the afternoon while the
ECMWF and Canadian show several shortwaves moving through the
area, with each shortwave bringing 0.10 to 0.25 of liquid precip
due to llvl instability and some dynamics. Increased POP between
50 to 70 percent across most areas, with the Laramie valley around
30 percent due to downslope flow. Even with some snow above 6500
feet, do not expect much accumulation in the valleys. May need
another Winter Weather Advisory for the mountains for 5 to 10
inches of snow Thursday.

.LONG TERM...(Thursday night through Tuesday)
Issued at 205 PM MDT Tue Apr 25 2017

Active pattern continues through early in the weekend then we see
a brief break on precipitation Sunday, then back to an active
northwest upper flow pattern early next week. Models showing an
upper low closing off over southeastern Wyoming and eastern
Colorado Thursday night with the GFS farther north and the ECMWF a
bit farther south. In both solutions the potential for significant
snowfall across parts of our area exist, with the GFS solution
producing several inches of snowfall across the northern part of
the Laramie Range where a foot of snow may fall through Saturday
given a favorable position of the low. If the GFS solution pans
out, we may see several inches of snow along the Pine Ridge as
well Thursday night into Friday...something to watch. A few inches
of snow possible for the lower elevations Friday night into
Saturday as the main upper system moves off to the east and we tap
colder air.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1143 AM MDT Tue Apr 25 2017

Upper low over east central Wyoming at mid-day will make slow
progression eastward over the next several hours with wrap around
precipitations working south across eastern Wyoming through the
evening hours. Rawlins will likely see on and off rain/snow mix
through early evening before tapering off by late evening as the
low pulls out to the east...keeping them down periodically down to
IFR visibilities in snow showers and MVFR ceiling prevailing.
Scattered showers through the afternoon for Laramie becoming a bit
more widespread mid to late afternoon with MVFR ceilings. Farther
east expect rain showers with periodic thunder mixed in this
afternoon and early evening for Cheyenne, Scottsbluff and Sidney
where late morning sunshine has increased instability. To the
north wrap around IFR/MVFR cloudcover will prevail into late
afternoon for Alliance and Chadron with wrap- around precipitation
working in from the northwest late in the day.


Issued at 205 PM MDT Tue Apr 25 2017

No Fire Weather concerns due to high humidities, daily chances for
wetting rains, and cool temperatures this week. Some drier air
will move into the region late in the weekend.



WY...Winter Weather Advisory until 6 PM MDT this evening for WYZ112-



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