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Area forecast discussion 
National Weather Service Riverton Wyoming
308 am MST sun Nov 29 2015

Short term...Sunday through Tuesday night

One of my favorite movies when growing up was Willie wonka and the
chocolate factory. The everlasting gobstopper one of the center
piece candies of the movie. This was mentioned since we have what
seems to be an everlasting situation...snow. Some areas across the
state have had recorded snow every day since Wednesday. And this
looks to continue on Sunday as well. A persistent upper level low
over the state will continue to spin over the next 24 to 36 hours
and continue to bring some rounds of snow showers to much of the
state. This much we know. However...where the snow will fall is more
problematic. With the showery and possibly banded nature of the is very difficult Pin Point. In addition...the models are
usually terrible in handling them. So for now...we gave all areas at
least isolated snow showers through much of Monday with somewhat
higher probability of precipitation where the models have some agreement. As a
rule...amounts should be light. However...with the fluffy nature of
the snow and the high ratio of liquid to snow...a few areas may pick
up a few inches of snow where showers persist. Otherwise...the story
will be for the continuation of below normal temperatures and mainly
light wind. The coldest temperatures will once again be in the
valleys with inversions expected to continue to hold. Patchy fog
will also be possible each night and morning.

The pattern should finally break on Monday night as the upper level
low gets kicked out to the east and ridging begins to build across
the area. This should shut off the snow and allow for some clearing.
With increasing 700 millibar winds and tightening pressure gradient
some gusty southwest winds could develop across some of the favored
locations. This could warm temperatures by increasing mixing in some
of the favored areas like Rock Springs to Casper. However...the
deeper valleys should stay in inversions and keep temperatures well
below normal. And again...there will be the threat of fog in the
deeper valleys through the short term period.

Long term...Wednesday through Saturday upper ridge will prevail over the area Wednesday
and Thursday bringing dry weather and milder temperatures to the
mountains and wind corridors while some lower central basins and
western valleys will be colder with areas of fog under steep
inversions. The next Pacific trough will split along the West
Coast Thursday with most of energy headed south of the area with
only isolated to scattered snow showers expected across the west
with this system Friday and Friday night.

Discussion...forecast mostly in line with the European model (ecmwf) this morning
which shows better consistency in the development and timing of
split flow across the west Thursday through Saturday. GFS likely
overly progressive and putting to much energy in the northern stream
with incoming Pacific energy.

Upper ridge to be pumped up over The Rockies Wednesday and Thursday
as next Pacific trough approaches the West Coast. Strong warm
advection in the middle-levels will result much milder temperatures
over the mountains and mainly the Cody foothills and NE Johnson
County east of The Divide while lower central basins and western
valleys will likely be trapped under steepening inversions. These
inversions are likely to be especially pronounced over the snow-
covered Wind River basin where highs Wednesday and Thursday will
remain mostly in the 20s. On the other end of the spectrum
northeast Johnson County will likely see lower 50s for highs by
Thursday. Steepening inversions will also lead to fog formation
Tuesday night through Thursday morning with fog expected to be most
widespread across the Wind River basin and Upper Green river basin.
Upper ridge will translate the area Thursday with flow backing fog should become less extensive Thursday night...mainly
confined to lower river valleys.

European model (ecmwf) continues to take most of the energy with incoming Pacific
trough south into The Four Corners area Friday night. The
associated surface cold front will push into the west Friday and
across central Wyoming Friday night. Any snowfall accumulations in
the west are expected to be light with this system. The front
should be able to scour out most of the cold air lingering in the
lower Wind River basin. An upper ridge will then build over the
area next weekend.


Aviation.../12z issuance/

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

An upper level storm system will move across Wyoming today and tonight.
Areas of light snow will occur as the system moves through the
state. VFR to MVFR conditions will occur through tonight. Some
light snow or fog and low ceilings will cause the MVFR conditions.

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

An upper level storm system will move across Wyoming today and tonight.
Areas of light snow will occur as the system moves through the
state. VFR to MVFR conditions will occur through tonight. Some light
snow or fog and low ceilings will cause the MVFR conditions.

Fire weather...

A very slow moving area of low pressure will keep snowfall across
the area through the early portion of the week. Wind will remain
generally light through the weekend...keeping smoke dispersal
generally poor. Some of the mountain locations may see some gustier
wind with increased smoke dispersal. behavior will
remain low.

Riw watches/warnings/advisories...


Short term...hattings
long term...aem
fire weather...hattings

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