Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 221726
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1126 AM MDT Sun Apr 22 2018

.SHORT TERM...(Today through Tuesday)
Issued at 315 AM MDT Sun Apr 22 2018

Upper low that brought the rain and snow to the CWA yesterday was
located over central KS/OK overnight. A ridge extended from the
Upper Midwest southwestward through WY and UT. Light winds and
a moist boundary layer prevailed over much of southeast WY and
western NE. Areas of low clouds and patchy fog, locally dense at
times, continued along the Cheyenne Ridge into portions of the NE
Panhandle and east central WY. The fog and low stratus will linger
through early this morning.

Current short range models/ensembles are in good agreement with the
upper ridge sliding east into the Plains through Monday. After
the low clouds and fog dissipate this morning, skies will become
mostly sunny and temperatures will rebound quickly into the 50s
and 60s this afternoon. The only fly in the ointment will be
isolated afternoon showers relegated to the Snowy/Sierra Madre
mountains due to limited moisture and upslope. Winds will be
light under the influence of the high pressure ridge.

A Pacific Northwest upper trough and surface cold front will approach
WY late tonight, and progress east through southeast WY and western
NE Monday afternoon and evening. Winds will increase ahead of the
front, with good chances for rain showers and high elevation snow
showers spreading west to east through the morning and afternoon.
Instability has increased slightly from past model runs, with NAM
SBCAPE from 500-1000 j/kg Monday afternoon ahead of the cold
front. Kept mention of isolated t-storms in the weather grids most
areas Monday afternoon. High temperatures Monday will remain mild
with 60s to around 70 east of a line from Douglas to Laramie, and
50s to the west. It will be breezy ahead of and behind the cold
front Monday. Rain changes to all snow Monday night as the colder
air infiltrates the region.

Precipitation will be slow to exit the CWA Tuesday, with the NAM
and Canadian models developing a closed upper low in the vicinity
of eastern WY and western NE/SD. The GFS and ECMWF maintain an
east to west trough axis across WY and western NE. Morning rain
and snow showers will taper off from west to east Tuesday afternoon.
It will be blustery and much cooler Tuesday with high temperatures
in the 30s and 40s. Total snow accumulations from Monday through
Tuesday will range from 1 to 3 inches mountains and east central
WY, to less than an inch elsewhere.

.LONG TERM...(Tuesday night through Saturday)
Issued at 315 AM MDT Sun Apr 22 2018

Any lingering pcpn will end Tuesday evening as the upper low moves
farther away over the central plains. Dry and warmer Weds as a short
upper ridge passes across the region. Next shortwave drops south out
of Canada and across the region Thursday bringing a cool front and
scattered rain/snow showers mainly to the mtns. Relatively fast moving
system should keep precip amounts on the light side. Upper ridging
returns to the area for Friday and Saturday boding for quite mild
temperatures both days. Could see some showers mainly around the mtns
by late Saturday, with a few tstms possible as well.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1124 AM MDT Sun Apr 22 2018

Wyoming TAFS...VFR. Wind gusts to 24 knots at Cheyenne through
00Z, then wind gusts to 22 knots at Rawlins after 15Z Monday.

Nebraska TAFS...VFR at Chadron and Alliance. MVFR at Scottsbluff
and Sidney through 19Z, then VFR.

&&

.FIRE WEATHER...
Issued at 315 AM MDT Sun Apr 22 2018

A ridge of high pressure will dominate the districts today and tonight
with milder and drier conditions. Isolated afternoon showers are possible
over the Snowy and Sierra Madre mountains. Lowest humidities will range
from 15 to 20 percent over northwest Carbon County this afternoon. However,
winds will be light. The next Pacific low pressure system and cold front
will bring a good chance of rain showers, high elevation snow showers,
and gusty winds Monday. Isolated thunderstorms are also possible. Rain
will change to snow Monday night behind the front and linger into Tuesday.
It will be breezy and much cooler Tuesday.

&&

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

$$

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



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