Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 171128

Area Forecast Discussion
National Weather Service Cheyenne WY
528 AM MDT Sat Mar 17 2018

Issued at 525 AM MDT Sat Mar 17 2018

Visibility has been persistently low along the Platte River Valley
in the southern Panhandle through Torrington this morning.
Visibility report at 1/4 mile at Scottsbluff and Torrington for
quite some time now and do not see any reason it would not
persist. Decided to issue a Dense Fog Advisory to cover the
problem through mid morning. Updates have been sent.


.SHORT TERM...(Today through Monday)
Issued at 317 AM MDT Sat Mar 17 2018

Forecast challenges deal with another snow event expected Sunday
into Monday morning.

Currently...Water vapor imagery showing upper low pressure system
over south central Oregon this morning. Surface low analyzed over
northern Utah and northeastern Nevada. CWFA pretty much clear so
far on IR imagery for now.

Today...Split energy from the Oregon low through the day today
with northern energy moving up into northwestern Wyoming and
southern energy pushing south into western Colorado. Looking for
increasing mid and high level clouds through the day today. Today
will be dry as precip ahead of low spreads into southwest Wyoming
and northwestern Colorado late this afternoon. A pretty nice day
with highs in the mid 40s west and mid 50s east.

Southern energy begins to move into western Colorado Sunday
morning and eventually eastern Colorado by Sunday afternoon.
Surface low begins to deepen vicinity of Denver or maybe slightly
south. GFS isentropic surfaces begin to show upglide across our
western counties by 18Z, becoming strong towards the afternoon
across our southern zones (the I-80 Corridor).

Superblend snow levels too high once again with this system as GFS
700mb temperatures fall to -6 to -8C Sunday afternoon. Decided to
use NAM snow levels with this event, which produces all snow.

Getting pretty good snow amounts across our southern zones Sunday
afternoon/evening into Monday morning. Getting warning level snow
amounts for the Snowy Range and south Laramie Range, so decided on
issuing a Winter Storm Watch for these two zones. Advisory level
snow amounts for eastern foothills, Laramie and zones surrounding
the Snowy and Sierra Madre Ranges. Later shifts will likely need
to issue advisories for these areas as well as the Sierra Madre
Range and if heavy snow still looks likely, warnings for the Snowy
Range and south Laramie Range.

Upper low tracks into western Kansas by Monday morning. This track
a little further south than this past low, so most of the snow
should stay in our southern zones. GFS hits the southern Panhandle
pretty hard Monday morning, so likely to need winter headlines out
there as well.

.LONG TERM...(Monday night through Friday)
Issued at 317 AM MDT Sat Mar 17 2018

A trend to drier and milder weather will occur by midweek as upper
ridging builds over the western CONUS Tuesday and moves east to
the plains states by late Thursday. A weak impulse ahead of the
building ridge may bring a few snow showers mainly to the mtns
Tuesday. Max temps a little above seasonal averages Weds and
Thursday. The next upper trough looks to affect the region late
Thursday through Friday with pcpn returning mainly over western
parts of the CWA then.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 457 AM MDT Sat Mar 17 2018

VFR prevailing through the period at the terminals except for some
patchy fog and low clouds affecting mainly KAIA and KBFF this
morning. Some gusty winds at KRWL and KLAR this afternoon with gusts
over 35 kts possible.


Issued at 317 AM MDT Sat Mar 17 2018

A pretty nice day today as high pressure dominates the area.
Expect dry weather and fairly light winds. Another low pressure
system tracks across Colorado Sunday with accumulating snow
returning to the I-80 Corridor from Sidney to Rawlins through
Monday morning. Should the low track further north than current
forecast, then more of our northern Fire Weather Zones could see
accumulating snowfall. Fire weather concerns through Tuesday will
be low with existing snowpack, additional snow and cold


WY...Winter Storm Watch from Sunday morning through late Sunday night
     for WYZ114.

     Winter Storm Watch from Sunday afternoon through late Sunday
     night for WYZ116.

     Dense Fog Advisory until 10 AM MDT this morning for WYZ108.

NE...Dense Fog Advisory until 10 AM MDT this morning for NEZ003-



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