Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 251753
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1153 AM MDT Tue Apr 25 2017

.UPDATE...This Afternoon

Added Thunderstorms to this afternoons forecast as convection has
developed along and just north of the I-80 corridor. Model
soundings show just enough instability and CAPE to warrant mention
of thunder through early this evening. These showers and
thunderstorms will gradually move east south east across the area.
Brief heavy downpours and small hail are possible.


.SHORT TERM...(Today through Thursday)
Issued at 312 AM MDT Tue Apr 25 2017

Today...Although it appears that significant snowfall has ended or
decreased across our Snowy and Sierra Madre Ranges overnight, the
models are indicating another lobe of energy or shortwave trough
aloft swinging near the mountains this afternoon, with more snowfall
expected during the afternoon, thus will continue the winter weather
advisory.

With the next cold front progged to move north to south across our
counties today, and this aforementioned lobe of energy swinging
across southeast Wyoming in the moist airmass, expect scattered to
numerous showers to once again develop this afternoon aided by the
cold frontal lift and baroclinic band. Even cooler temperatures
today in the wake of the cold front and with plenty of clouds and
precipitation around.

Tonight...Areal coverage of showers will decrease, especially after
midnight, as the shortwave trough moves off to our southeast and the
low and mid levels of the atmosphere dry out somewhat.

Wednesday...Although no significant lifting mechanisms are obvious
in the model data, an increase in orographics is expected as more
moisture moves our way with isolated to scattered showers in the
afternoon primarily west of a Douglas to Laramie line.

Wednesday night...Next shortwave trough aloft moves to southwest
Wyoming spreading clouds and showers across our western counties,
west of a Douglas to Cheyenne line.

Thursday...The shortwave trough aloft moves across our counties, and
with abundant low and mid level moisture present, we anticipate
scattered to numerous showers to once again develop in the unstable
airmass. Model guidance high temperatures look reasonable and have
compromised with the NAM and GFS MOS maximums for high temperatures,
producing yet another cool late April day with abundant cloud cover
and showers.

.LONG TERM...(Thursday night through Monday)
Issued at 312 AM MDT Tue Apr 25 2017

An upper level trough will dig north to south along the Rockies
Thursday night through Saturday as a strong upper jet dives south
across the Great Basin. Our forecast area will remain in cyclonic
flow through this time with an inverted sfc trough positioned along
the spine of the mountains initially. This sfc trough will be pulled
south as a cold front in response to deepening sfc low pressure over
the southern plains within the digging upper trough. Will see a good
chance for a rain/snow mix over much of the CWA through this time.
Precip should remain all snow above toughly 7500ft, with some
moderate accumulations likely in the higher peaks. In the lower
elevations, should be a cold rain during the daytime hours changing
to snow during the overnight time period with some accumulation
possible. This system will shift to the east Saturday night into
Sunday with warmer and drier northwest flow moving overhead. A
slight chance for rain and high elevation snow returns late Monday
as a vigorous upper trough approaches from the northwest.

&&

.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.

&&

.FIRE WEATHER...
Issued at 312 AM MDT Tue Apr 25 2017

No concerns due to relatively high humidities and precipitation
through the end of the week and into the weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 PM MDT this evening for WYZ112-
     114.

NE...None.
&&

$$

UPDATE...TJT
SHORT TERM...RUBIN
LONG TERM...RJM
AVIATION...JG
FIRE WEATHER...RUBIN


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