Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211739

Area Forecast Discussion
National Weather Service Cheyenne WY
1139 AM MDT Sat Apr 21 2018

Issued at 1025 AM MDT Sat Apr 21 2018

Advisories expired for the Snowy and Sierra Madre Ranges earlier
as the low pressure system tracks into southwest Kansas this
morning. Still getting snow over the south Laramie Range with low
visibilities. Will keep this advisory going til noon.

UPDATE Issued at 450 AM MDT Sat Apr 21 2018

Snowfall trends have been declining during the past few hours west
of Cheyenne, and increasing east of Cheyenne. Additional snowfall
of one to two inches is forecast for elevations above 8000 feet,
as well as from Laramie County WY east to Cheyenne County NE.
Impacts to area roadways have been limited to poor visibility in
patchy dense fog from Cheyenne to the I-80 Summit, as well as some
slush/slick spots.

Cancelled the Winter Weather Advisory for Arlington/Elk Mountain,
and downgraded the Winter Storm Warning to a Winter Weather Advisory
for the Snowy Range this morning.


.SHORT TERM...(Today through Monday)
Issued at 245 AM MDT Sat Apr 21 2018

Overnight water vapor loop showed the upper low situated over south
central CO, with mid/upper moisture rotating cyclonically into the
CWA. Large scale lift and moist upslope low level flow continued to
produce a mixed bag of precipitation, from light rain/freezing rain
to snow/snow pellets. Accumulations for the most part have been
confined to grassy surfaces, with some slushy spots developing on
roadways, including I-80 between Cheyenne and Rawlins. Mountain
SNOTELs estimated less than 6 inches of snow thus far, however
additional snowfall of 1 to 3 inches is forecast through early this
morning for elevations above 8000 feet. Valleys and high plains can
expect up to an inch of snow.

General consensus amongst the 00Z short range models/ensembles progs
the CO upper low to track slowly east into the central/southern Great
Plains today. Rain and high elevation snow will persist this morning
east of a Lusk to Rawlins line, then taper off from west to east this
afternoon. Winter Weather Advisories remain in effect for the South
Laramie Range, North Snowy Range foothills and Sierra Madre Range,
and a Winter Storm Warning for the Snowy Range this morning. High
temperatures today will range from 30s and 40s with clouds and
precipitation, to the 50s across portions of east and south central

Previous model runs were hinting at moist southerly flow and low clouds
lingering through late tonight from the South Laramie Range eastward.
Latest models indicate southwesterly low level winds tonight that
would preclude low cloud development. On Sunday, the CWA will be
under the influence of a high pressure ridge with drier and warmer
weather. High temperatures will average near seasonal normals. Surface
winds will be light through the day.

The next upper trough and cold front will be moving onshore into the
Pacific Northwest Sunday morning, progressing eastward across the
northern Rockies Monday morning and across WY and western NE Monday
afternoon and night. Showers develop over western WY Monday morning,
spreading east across the CWA Monday afternoon. There may be some
instability for isolated thunder, but left out of the weather grids
for now. It will be breezy ahead of and behind the cold front. High
temperatures will range from the 60s east of the Laramie Range, to
the 40s and 50s west.

.LONG TERM...(Monday night through Friday)
Issued at 230 AM MDT Sat Apr 21 2018

Upper trough will slip slowly southeast across the CWA Monday night
and Tuesday with a decent push of colder air associated with it. Some
rain and snow expected especially over northern and eastern parts of
the CWA, tapering off late on Tuesday. Mild and dry Weds as a short
wave upper ridge moves across the region then the next upper short
wave passes across Thursday bringing another round of pcpn and cooler
air. Warmer and dry weather returns for Friday on the front side of
an upper ridge over the western CONUS.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1127 AM MDT Sat Apr 21 2018

Wyoming TAFS...VFR at Rawlins. Occasional IFR at Laramie until
20Z, then MVFR until 01Z, then VFR. MVFR at Cheyenne until 20Z,
then VFR.

Nebraska TAFS...MVFR at Chadron until 00Z, then VFR. Occasional
IFR at Alliance until 20Z, then VFR until 10Z, then IFR until 15Z,
then VFR. IFR at Scottsbluff until 20Z, then MVFR until 01Z, then
VFR until 09Z, then IFR until 15Z, then VFR. IFR at Sidney until
21Z, then MVFR until 08Z, then IFR until 15Z, then VFR.


Issued at 215 AM MDT Sat Apr 21 2018

Low pressure at the surface and aloft over Colorado early this morning
will slowly track east today with rain and snow gradually tapering
off from west to east this afternoon. No fire weather concerns today
with wetting precipitation and cool temperatures. Drier and milder
conditions will return Sunday. Lowest afternoon humidities Sunday will
range from 15 to 20 percent across western Carbon County, however fuels
and wind speeds will be non-critical. Another Pacific low pressure
system and cold front will bring good chances for showers and cooler
temperatures Monday and Monday night.




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