Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 231227
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
527 AM MST Mon Jan 23 2017

.SHORT TERM...(Today through Tuesday night)
Issued at 527 AM MST Mon Jan 23 2017

The Pacific storm system is moving east into the western CONUS
this morning, while the 150kt southwest jet out ahead of the
system is steadily sagging south of our forecast area. Overnight,
light snow showers progressed eastward across the area, with areas
of reduced visibility observed in snow and gusty southwest winds
from the Arlington area westward to Rawlins. Expect snow to
continue for much of Carbon and Albany Counties today and tonight
as this area will experience the combination of mid-upper level
diffluence in advance of a shortwave trough, southwesterly upslope
flow, a bit of instability, and frontal forcing when the sfc cold
front slowly makes its way south. Think snow totals are still on
par for mountains, but bumped up PoPs and snow for the surrounding
lower elevations as there is some concern that enhanced banding
will develop across central and northern portions of Carbon and
Albany Counties this afternoon. Added these areas into the Winter
Weather Advisory for the likelihood of 2 to 5 inches, with higher
amounts in the Northern Laramie Range. Not confident Laramie will
see much snow as the valley will most likely remain shadowed by
the Snowy Range initially, while the front remains to the north
during the time the strongest upper forcing moves overhead. A few
snow showers should bring light accumulations to Laramie late this
afternoon, and again on Tuesday as the front finally moves south,
but not enough to warrant inclusion in the Advisory at this time.

The track of the storm through Tuesday night still looks
consistent with previous model runs, although there remains some
differences with position of the low as it deepens over the
central plains. The GFS and NAM are more aggressive and further
north with the low than the ECMWF. Therefore, made little change
to the forecast for eastern portions of the forecast area. The
only major change is the inclusion of Niobrara County into the
Winter Storm Watch. Thinking southeastern sections of the County
will see enhanced snowfall in subtle upslope flow and gusty
northwest sfc winds on Tuesday afternoon, similar to locations
further east in Sioux and Dawes Counties. Further south, models
are painting a bit more QPF with the cold front as it drops south
late tonight through Tuesday morning, so may have to consider
expanding Advisories for this areas as well. However, strong
northwest downslope flow may still keep accumulations on the
lowside near the Colorado border.

.LONG TERM...(Wednesday through Sunday)
Issued at 527 AM MST Mon Jan 23 2017

Cold northwesterly flow aloft will be in place on Wednesday and
Thursday with 700 mb temps around 17C.  This means that highs will
struggle to get out of the 20s over much of the area.  Light
orographic snows will be possible through Wednesday night over the
Sierra Madre and Snowy Ranges.  Heights aloft begin to rise by
Friday and Saturday as a large upper level ridge develops across the
Pacific Northwest and a drier airmass will move into Wyoming.  Temps
do not really increase back to normal until the weekend.  While
breezy conditions will exist most days, not expecting any high wind
threats through the extended period as the 850mb CAG-CPR gradient
mostly remains below 40 meters.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 527 AM MST Mon Jan 23 2017

Light snow showers will continue to occur at RWL through much of the
TAF period with prevailing MVFR vis, and brief periods of IFR vis.
The snow showers will spread to areas east of the Laramie Range
after 00-06Z.  Southwest winds will be breezy at RWL/LAR through the
afternoon with gusts to 20-30 kts.

&&

.FIRE WEATHER...
Issued at 527 AM MST Mon Jan 23 2017

No Fire Weather concerns through the week due to temperatures
near or below normal and widespread snow today through Tuesday
night.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 PM MST Tuesday for WYZ112-114.

     Winter Storm Watch from late tonight through Tuesday evening for
     WYZ102.

     Winter Weather Advisory until 11 AM MST Tuesday for WYZ103>105-
     109>111-113.

NE...Winter Storm Watch from late tonight through Tuesday evening for
     NEZ002-095.

&&

$$

SHORT TERM...RJM
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...RJM



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