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Area forecast discussion 
National Weather Service Riverton Wyoming
403 PM MST sun Nov 29 2015

Short term...tonight through Monday

The elongating area of low pressure continues to generate light
snowfall this afternoon. Most activity has been noted across the
north and west...but periods of light snow have been observed
across central Wyoming as well.

These sporadic snow events will continue under the influence of
this system through Monday morning. Widespread light
precipitation chances remain in the forecast...with higher chances
included for the central and western mountains. The core of the
low pressure will shift east of the forecast area Monday
afternoon. This may alleviate some of the widespread
potential...but light snowfall will remain possible with
wraparound moisture.

Long term...Monday night through Sunday

The pesky upper level cut off low will slowly eject east into the
Central Plains Monday night...stronger northwest flow will move in
behind the low. This will be a tricky period as the cold pool aloft
will weaken the inversions over night followed by stronger northwest
sinking winds. The question will be can the winds mix down and blow
out the weakened inversions in the valleys and basins? The higher
resolution models do show the northwest winds intrude from northwest
to southeast across the Wind River and Upper Green river basins as
well as across the western Bighorn Basin. Temperatures will modify
through the extended and remain the biggest forecast challenge.
While temperatures are likely to be below normal...they may end up
not as bitter as the current conditions. High pressure will move in
Tuesday and Wednesday as the cut off low drifts east northeast over
the Great Lakes...while a large trough deepens from the Gulf of
Alaska south off of the West Coast. This will be a dry period with
variable cloud cover. By Thursday warming will become more
significant as the ridge axis shifts to the east and increasing
southwest flow moves into the west. This will intensify on Friday
with windy areas likely to develop along and near the east slopes of
the mountains and through the wind corridor across Sweetwater...
southern Fremont and Natrona counties. Stronger downslope winds are
also likely in Park County in the Cody foothills. Some snow showers
should work into the western mountains as Pacific moisture streams
into the west in the increasing southwest flow. Friday should see
significant warming...especially in the windy downslope areas.
Friday night and Saturday the long wave Pacific trough will pass
while it splits. This will limit snowfall but the western and
northern mountains should see some snowfall before high pressure
ridges in from the northern Great Basin Saturday. Temperatures
should be cooler behind the trough...which should kick a weak cold
front south across the area with an end to the strong southwest
winds. Sunday should be dry.


Aviation.../00z issuance/

East of The Divide...kcod/kcpr/klnd/kriw/kwrl routes

Periods of light snow will persist through much of the taf period.
Kwrl and kcod appear to be the most favored locations for snow
development...though no area is completely unlikely. Snow
development may bring periods of MVFR conditions...with IFR
conditions possible over the Big Horn basin. Patchy morning fog
will also be possible after 12z...with activity lifting by 18z.
Mountain tops will remain obscured. Forecast models do attempt to
bring in some clearing conditions after 20z...but confidence was
not high enough to remove the mention of at least vcsh through 00z

West of The Divide...kbpi/kjac/kpna/krks routes

Periods of light snow will persist through much of the taf period.
Kjac appears to be the most favored location for more persistent
snowfall and associated MVFR to IFR conditions. However...snowfall
will continue to develop southward to include kbpi and kpna.
Additionally...this system remains fairly unsettled leaving the
potential for some snow development across the entirety of the
area west of The Divide. Snow development may bring periods of
MVFR conditions for impacted terminals. Patchy morning fog will
also be possible after 10z Monday and should lift by 18z.
Mountain tops will remain obscured.


Fire weather...

Fire behavior will remain low under the continued influence of low
pressure. Light snowfall will remain possible across much of the
area...with better likelihoods over the mountains. Conditions
looks to improve Monday evening as the area of low pressure moves
further east of the state. This will permit a drier north to
northwest flow to develop...bringing drier conditions and
initiate a slight warming trend.


Riw watches/warnings/advisories...


Short term...branham
long term...c.Baker
fire weather...branham

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