Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 292147 CCA
AFDCYS

Area Forecast Discussion...Corrected
National Weather Service Cheyenne WY
312 PM MDT Sat Apr 29 2017

.SHORT TERM...(This evening through Monday night)
Issued at 300 PM MDT Sat Apr 29 2017

Afternoon water vapor imagery loop showed a deep upper low pressure
system over central NM, with strong diffluent flow extending northward
across the central/southern high plains. The strongest upper forcing
and lift was over CO/NM. Regional radars detected the the northern
extent of wrap-around precipitation from northeast CO into southwest
NE. Brief light snow or flurries lingered along and south of the I-
80 corridor from east of Rawlins to Laramie and Sidney. Temperatures
ranged from the mid 20s to mid 40s with northeasterly winds 10 to 20
mph.

The 12Z models are in good agreement through the short term. The
southern Rockies upper low will track northeast across the Central
Plains toward the Upper Midwest through Monday. Northwest flow aloft
will dominate the region Sunday through Monday night. This will open
the door for a couple of upper level troughs to track southeast across
the northern Rockies and Plains.

Lingering light snow or flurries near the CO border will end by sunset.
Skies will clear with diminishing winds tonight. It will be cold with
low temperatures in the teens and 20s. As the central Plains low
intensifies Sunday, a tight pressure gradient will generate stronger
northwest winds, especially from the southeast WY plains into the
NE Panhandle. Gusts of 30 to 40 mph are likely from late morning
through the afternoon. High temperatures Sunday will be 5 to 10
degrees warmer compared to Saturday, but still below seasonal normals.

Some Pacific moisture will spread into western WY Sunday afternoon,
arriving over south central WY Sunday evening. Scattered rain/snow
showers develop and spread east to the Laramie Range as snow late
Sunday night. Snow showers will continue above 8500 feet Monday,
with rain showers for the southeast WY and northern NE Panhandle.
A tight pressure gradient will generate rather gusty northwest winds
Monday afternoon for much of the CWA. Below average high temperatures
are forecast Monday with 40s and 50s. Scattered rain/snow showers
will continue across much of south central and southeast WY Monday
night.

.LONG TERM...(Tuesday through Saturday)
Issued at 300 PM MDT Sat Apr 29 2017

Tuesday...Expect a quite wet and cool day as the next shortwave
trough aloft moves southward across Wyoming acting on a moist low
and mid level atmosphere. Greatest coverage of showers should be
along and west of Interstate 25.

Wednesday...Decreasing areal coverage of showers as the shortwave
trough aloft moves to the south of our counties and the atmosphere
begins to dry out. A bit warmer with more sunshine and less
precipitation.

Thursday...Strengthening ridging aloft will aid in producing a
considerably warmer day with maximum temperatures in the 60s to
lower 70s at lower elevations. Continued dry with lack of low and
mid level moisture.

Friday...Warmest day of the week as the ridge aloft moves off to our
east with a developing surface lee trough and warmer temperatures
with downsloping.

Saturday...Continued mild as the ridging aloft prevails and minimal
low and mid level moisture continues. We may have enough mid level
moisture and daytime heating to induce isolated late afternoon and
early evening showers from near Douglas to Laramie.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1143 AM MDT Sat Apr 29 2017

Wyoming TAFS...VFR prevails, except for occasional MVFR at Laramie
and Cheyenne until 20Z today. Wind gusts to 25 knots through 00Z...
then wind gusts to 30 knots after 15Z Sunday.

Nebraska TAFS...VFR. Wind gusts to 35 knots after 15Z Sunday at
Alliance, Scottsbluff and Sidney. Wind gusts to 34 knots at Sidney
from 20Z today until 02Z tonight.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Sat Apr 29 2017

Lingering light snow or flurries near the Colorado border will end
by sunset. After a cold night, Sunday will be breezy and milder.
Moist fuels from recent precipitation and higher relative humidities
will negate fire weather concerns. Periodic rain and snow shower
activity and cool temperatures will prevail for the first half of
next week with the passage of a few upper level low pressure troughs.
Much warmer and drier conditions can be expected district-wide for
Thursday and Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...MAJ
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...MAJ



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