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fxus65 kriw 201821 

Area forecast discussion
National Weather Service Riverton Wyoming
1121 am MST Wed Nov 20 2019

Short term...(today through thursday)
issued at 400 am MST Wed Nov 20 2019

A cold front early this morning roughly from Thermopolis to
Hiland will push to the Continental Divide by 6 am, and then surge
southwest across southwest Wyoming by 9 am. The front is not
ushering a bitter cold airmass into the area, but after well
above average temps the last few days it will feel like a return
to winter.

A shortwave trough with pseudo-tropical moisture over southern
Arizona will pull northeast into The Four Corners by midday and
then into the High Plains of Colorado/Nebraska. As this occurs,
moisture from this shortwave will spread northward over the cold
front. Snow is expected to develop quickly this morning over much
of the forecast area with an emphasis across central and southern
areas. At the same time, models are showing decent upslope flow
over in typical areas such as Lander foothills and Casper. Also
there is upslope flow across portions of southeast Lincoln into
southwest Sublette County. These upslope conditions should result
in enhanced snowfall in those areas. Strong northerly to easterly
winds will occur in wake of the cold front with persistent 3 to
6mb rises every 3 hours through mid evening.

The heaviest snow looks to occur from 9 am to 9 PM today, with
much lighter snow for the remainder of tonight into Thursday
morning. In wake of the initial shortwave trough exiting into the
plains, dynamics and the overall wind pattern will weaken
relatively quickly. Strong easterly winds over the south will keep
hazardous conditions going into Thursday morning. The rest of the
area farther north (wind river basin/Natrona county) could have
little weather impacts for the Thursday morning commute. Expect
roads to be slick, but snow will be very light, and winds look to
be relatively light.

For winter highlights, have issued a winter wx advisory for the
Upper Green river basin (big piney), and upgraded S. Lincoln
County. The easterly flow is expected to enhance snowfall along
the Wyoming Range, and areas generally east of Kemmerer. Also
winds will be quite strong over S. Lincoln which is enough to
upgrade them into a warning. Otherwise no changes for the rest of
the zones.

As a deformation axis pulls south on Thursday, the light snow will
come to an end, and the winds over the south will gradually
decrease. The strong easterly winds over the south will weaken
midday into Thursday afternoon as the surface pressure gradient

Long term...(thursday night through wednesday)
issued at 323 am MST Wed Nov 20 2019

With a fresh snowpack, Friday morning lows will be cold with the
basins likely in the single digits. Temperatures will attempt to
recover but lower elevations with fresh snow may struggle to warm up
through the weekend. Breezy conditions are likely Saturday and
Sunday afternoon from South Pass to Lander as well as the upper Wind
River basin.

The next system will reach the state on Sunday night as
a shortwave with Pacific moisture arrives from the northwest. A cold
front will sweep from the north Sunday night through Monday. This
will allow for another round of snow, this time looking most
favorable across western Wyoming. All areas currently look to get a
shot at snow, however, and models keep snowfall at least through
Monday before solutions become more diverse. The GFS keeps precip
associated with this system into Tuesday afternoon before
clearing, while the European model (ecmwf) moves it out Monday night. However, the
European model (ecmwf) has the next system knocking on the door by Tuesday night,
with the potential for a stronger snow event Wednesday across the
state. Regardless of finer details at this point, this active
winter pattern will continue through the period.


Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1047 am MST Wed Nov 20 2019

For locations in northern Wyoming including kwrl and kcod, as well
as kbpi, kjac, kcod, kpna in the far west, snow showers may
linger until this evening, but will be light and VFR/MVFR
conditions are expected throughout the period. At kjac, kcod and
kwrl gusty winds diminish around the same time as the snow showers
end. Ceilings lift and skies begin to clear by 12z for these

For locations in the southern Wyoming, including krks, as well as
areas east of The Divide, including kcpr, klnd, and kriw, snow
has begun to move in and will continue to increase into the
afternoon. MVFR/IFR conditions are expected as the snow builds in.
Snow ends around 10z Thursday but visibilities improve by late
this evening and MVFR/VFR conditions are expected to return. Kriw
may see occasional low end VFR conditions throughout the period,
as a result of being in the "snow shadow" of The Owl creek
mountains. Krks will continue to gust 30 to 20 knots throughout
the period. For other locations, winds will die down this
afternoon into the evening.


Fire weather...
issued at 400 am MST Wed Nov 20 2019

Snowfall is expected today with the bulk of the snow occurring
across central and southern areas in wake of a strong cold front.
Smoke dispersal will generally range from poor to fair, except
good where windy conditions are expected. The snowfall will
gradually end in most areas by late tonight into Thursday morning.
Most areas will be dry with decreasing cloudiness Thursday
afternoon. Smoke dispersal will be poor across the area on


Riw watches/warnings/advisories...
Winter Storm Warning until 11 am MST Thursday for wyz015-018-019-

Winter Weather Advisory until 11 am MST Thursday for wyz017-020-

Winter Weather Advisory until 5 am MST Thursday for wyz005-



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