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Area forecast discussion 
National Weather Service Riverton Wyoming
337 am MDT Wednesday Oct 22 2014

Short through Friday night

A cooler airmass hanging around today behind the cold front that
passed through overnight with some moderation on Thursday and
Friday. After a relatively calm day today...Thursday is expected to
be another windy day as a tug of War ensues between the cold but
dynamic trough to our northwest and the ridge poking in from the
south. Models have been trending further south with the
strengthening jet to our northwest on Thursday...which could
introduce stronger winds across the northern mountains and a slight
chance for precipitation. As the influence of the right exit region
of the jet intrudes Thursday afternoon through Friday...this will
kick up the mountain wave potential over the absarokas...maintaining
consistency with the day shift forecast for some wind gusts in the
western Cody foothills at 50 miles per hour for late Thursday or Thursday night
into Friday morning. Also bumped up probability of precipitation a little for the northwest
on Thursday night and Friday as a wave moves through. Most of the
action will remain to our west but there could be a few showers
around Yellowstone and The Tetons. Otherwise western and central
Wyoming will be dry and breezy through the period with above normal

Long term...Saturday through Wednesday
synopsis...unseasonably warm and breezy to windy conditions will
prevail on Saturday with record or near record highs possible. A
cold front will push across the area Sunday and Sunday night
spreading rain and snow showers and colder temperatures across the
area into Monday. A westerly flow will bring mainly dry and
seasonable mild conditions on Tuesday and Wednesday.

Discussion...complex vortex over the Gulf of Alaska this morning
will wobble southeast to the West Coast Saturday morning. Medium range
models continue to handle the individual vortices within this
complex differently...but agree that a very warm SW flow will
prevail over the area Saturday between this system and strong
downstream ridge over the plains. Record high territory for the
25th is generally 72-74f range across central Wyoming for the 25th...a
bit warmer at wrl at 79f. Forecast highs are currently near or
exceeding these records.

On the 22/00z GFS and European model (ecmwf) runs...GFS continues to eject lead
shortwave out of base of the trough NE into western Montana
Saturday night while the European model (ecmwf) shows a more split
system...swinging this shortwave further south across the Great
Basin Saturday night. GFS version would keep most of the
precipitation confined to the west during the day Sunday with
windy and mild conditions across the central and south. European model (ecmwf)
depiction would result in much cooler and wetter conditions across
the area Sunday. Ec and GFS ensemble means favor slower
progression...more respect for strong plains ridge.
However...either way much colder air will spill into the area
Sunday night behind the front with snow levels expected to be
between 5-6kft by Monday morning. The northern third of the area
stands the best chance for some accumulation Monday
morning...mainly on vegetation with wet roads below 6kft. Cool and
unsettled northwest flow will prevail on the back side of the trough
latter in the day Monday with the better moisture and instability
expected over the NE half of the County Warning Area. Zonal flow will develop
behind this trough Tuesday and Wednesday...bringing in milder
Pacific airmass along with some orographic precipitation in the


Aviation.../12z issuance/

Low clouds /020-050 kft above ground level/ and possibly some patchy fog across
northwest Wyoming /NW of a kafo-kpna-30w kcod line/ this morning
will be the main aviation hazard for this set of tafs. This would
primarily impact the kjac terminal...with ceilings at kjac probably
high MVFR to low VFR. Fog chances at kjac will be slim due to the
aforementioned stratcu deck. This fog/low clouds across the
northwest are expected to erode by around 18z. Otherwise...VFR
conditions will occur today with mainly sky clear skies and light winds.
After 00z...expect increasing middle/high level cloudiness and
strengthening mountain top winds with possibly some low level wind shear on the Lee
side of mountain ranges along the Continental Divide developing
after 06z. However not enough confidence or magnitude to include at
kcod or klnd at this time.


Fire weather...

The wind and the rain will clear out today with cool temperatures
remaining behind the front that passed through yesterday.
Temperatures rebound a bit on Thursday as high pressure builds in
from the south but it will be another breezy day in spots with
southwest winds of 15 to 25 miles per hour common between Rock Springs and
Casper and over the higher elevations. Southwest flow returns on
Friday with drier and warmer conditions remaining. There could be a
few gusts over 25 miles per hour in the afternoon between Rawlins and southern
Casper dispatch but most areas will have relatively light winds.


Riw watches/warnings/advisories...


Short term...Allen
long term...aem
fire weather...Allen

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