Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 220511
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1110 PM MDT Tue Mar 21 2017

.UPDATE...
Issued at 831 PM MDT Tue Mar 21 2017

The forecast overall is in good shape for the rest of tonight.
Just added in some fog for the southern Laramie Range, eastern
foothills, and Cheyenne proper tonight within moist south-
southeast flow up the Cheyenne Ridge and Laramie Range. This
includes I-80 from Cheyenne to the Summit, and I-25 from the CO
border to Chugwater. HRRR guidance has been consistent showing fog
in this area for tonight, and agree with this assessment as
south-southeasterly winds favor stratus and fog development here.
Expect visibility to be reduced to a mile or less in the fog.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 250 PM MDT Tue Mar 21 2017

Forecast challenges deal with a potential winter storm Thursday
night into Friday.

Currently...Stationary frontal boundary lays over southeast
Wyoming this afternoon. Radar showing fairly widespread shower
activity along the front that is moving northeast at 30 MPH.
Strong low pressure seen on water vapor imagery still off the
Oregon coast.

For tonight, upper shortwave tracking northeast lifts stationary
front to the northeast to our northern counties. Short range HRRR
guidance showing showers lifting to the northeast with drier
conditions across the south.

A pretty warm day Wednesday as westerly winds predominate the
area. 700mb temperatures climb to +6C with some downsloping off
the Laramie Range. Looking at highs upper 60s/low 70s for areas
east of the Laramie Range with low 60s west.

Thursday is going to be unsettled as the Pacific low moves into
western Colorado. Widespread upper level diffluence over south
central Wyoming with precip beginning Thursday afternoon across
Carbon and Albany Counties. 700mb temperatures still above
freezing initially Thursday afternoon, but as the low tracks into
eastern Colorado, temperatures fall quite quickly. By 06Z Friday,
700mb temperatures down to -5C across Carbon County. Anticipate
rain changing over to snow quite quickly Thursday night. Strong
northeasterly winds at 700mb. ECMWF showing 55-60kts over the
Laramie Range. GFS 700mb winds 35-40kts. So looks like we should
be getting some strong winds with the snow as well.

.LONG TERM...(Friday through Tuesday)
Issued at 250 PM MDT Tue Mar 21 2017

Generally mild and rather unsettled weather anticipated across the
CWA this period in a progressive flow pattern. Pcpn will end
slowly across the southeast part of the CWA Friday as a vertically
stacked low drifts slowly east across the Kansas/Oklahoma area.
Windy conditions Friday over the plains but easing by late in the
day. Dry weather Friday night into Saturday as a short ridge
moves by then the next shortwave will move across later Saturday
into Sunday bringing another round of rain and higher-elevation snow
showers. Brief lull again late Sunday into Monday then the next in
the series of shortwaves arrives for late Monday into Tuesday
returning rain and snow to the fcst then.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1110 PM MDT Tue Mar 21 2017

Winds will be southerly with gusts increasing to 20-30 kt. Moist
upslope flow will produce low stratus and areas of fog at KCYS after
09Z. KSNY and KAIA could have a similar stratus/fog problem, but
right now confidence is highest for only MVFR cigs. VFR is expected
elsewhere, but will watch conditions overnight for possible
expansion of MVFR/IFR across the plains. Once cigs lift Wednesday
morning, conditions should remain mostly dry and breezy through the
day.

&&

.FIRE WEATHER...
Issued at 250 PM MDT Tue Mar 21 2017

A stalled front over southeast Wyoming interacting with upper level
disturbances will produce scattered showers and isolated
thunderstorms this afternoon along and west of Interstate 25. The
front will shift east into the plains Wednesday as west to
southwest winds increase ahead of a stronger Pacific low pressure
system. This low will track east across the central Rockies and
plains Thursday through Friday bringing widespread rain and snow
to the districts. Minimum relative humidities the next few days
will range from 20 to 30 percent, with fair to good nighttime
recoveries.

&&

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

$$

UPDATE...RJM
SHORT TERM...GCC/DEL
LONG TERM...RE
AVIATION...MAJ
FIRE WEATHER...GCC



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