Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
1050 PM MST Wednesday Dec 4 2013
Short term...tonight through Thursday
Improving conditions expected through the forecast period overall.
Some lingering haze and light snow continues to be reported across
the area as the departing area of low pressure loses its influence
over the forecast area. As clouds lift today...some additional
areas of flurries and ice crystals will be found across the area.
This remains a concern through Thursday morning across much of the
As advertised for a few days...frigid overnight temperatures
expected across the area with values of negative teens common
across the forecast area. Any wind will enhance these already
hazardous temperatures. Those with outdoor interests are reminded
to dress in layers with minimal amounts of skin exposed...and to
take care of any outdoor animals during this period of Arctic air.
Because of the colder conditions overnight...expect at least
slightly cooler temperatures across the forecast area for Thursday.
Thursday looks to be generally quiet across the forecast area with
a building northwest flow. Models indicate mostly dry conditions
across the forecast area. The mountains may see some continued
flurry activity with some lingering low clouds.
Long term...Thursday night through Wednesday night
Overall...conditions will remain cold through most of the forecast
period. Lows will moderate some Saturday morning...with southern
portions ranging between 2 and 5 degrees below zero. Other than
that...most of the forecast area will have widespread negative high
single digit and teens through at least Tuesday morning. High
temperatures will remain in the positive single digits to lower
teens through this period as well.
The pattern evolves into a westerly flow by Friday morning...as the
next shortwave dives southward along the western coast. This system
will continue to dig south...bottoming out over The Four Corners by
Saturday night. As it digs Friday...it will pull Pacific moisture
across the western mountains...producing a slight chance for snow
due to the increased upslope. As the system makes its wat into the
Desert Southwest...the flow over the County Warning Area becomes more
southwesterly...spreading snow chances across southern portions.
Snow amounts will remain light...due to the relatively fast speed of
this system...and the limited amount of moisture that is advected
into the area.
By Sunday...this system will eject into the Central Plains and no
longer affect the cowboy state. However...another Arctic plunge will
quickly move into the northern rockies Sunday night and into Wyoming
by Monday morning. This will reinforce the already frigid conditions
across the forecast area. If there is any good news...it will be
that this system will leave a northwest flow pattern in its wake
Monday night into Tuesday. This will allow for the atmosphere to
become mixed...and moderate the Arctic airmass. However...this will
also mean gusty winds to cause this mixing. These winds will affect
northern portions...as well as Johnson and Natrona County. The Wind
River basin may be affected as well. There may be some changes with
this...due to the strength and location of the polar front
jet...that will help bring these winds.
Areas of MVFR ceilings and -sn...with local IFR conditions will be
encountered primarily west of The Divide and from vicinity kwrl-kcod
through 12z with these conditions becoming more localized after
15z. VFR conditions will prevail elsewhere with local IFR/MVFR ice
and fog partially obscuring the terrain.
A weak shortwave will push southeast across the west from 22z Thursday-06z
Wednesday spreading areas of MVFR -sn into vicinity kjac around 22z and
southeast across vicinity kbpi-krks 23z Thursday-03z Friday. These conditions will
persist through Thursday night. VFR conditions will prevail east of
The Divide with local MVFR/IFR ice and fog forming once again after
The advertised Arctic airmass will leave frigid temperatures
across the forecast area overnight. Values in the negative teens
will be common. With th colder start to the day...expecting cooler
daytime temperatures on Thursday...though conditions will mostly
be dry. A few flurries may be possible as clouds continue to lift
across the area. The next opportunity for wintry precipitation
will be Friday...mainly across the western mountains and valleys.
Expect below normal temperatures to persist into the weekend.