Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 161016
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
316 AM MST Mon Jan 16 2017

.SHORT TERM...Monday through Wednesday night

According to the calendar, Groundhog Day is still more than 2 weeks
away. However, over the past several days, the weather has felt
like Bill Murray`s character in the classic 1993 movie. And yes,
Bill Murray was a weatherman in that movie. Was he a meteorologist?
That is not known. In other words, very similar each day. Today
will be another day with chilly temperatures in the Basins and
warmer conditions in the windier areas where the atmosphere can
mix. There will also be some patchy fog around like previous
nights. However, widespread dense fog looks less likely in
Sweetwater County due to a bit more wind and some mid level clouds
around. We will continue the dense fog advisory for now as it is
still foggy west of Rock Springs as of 200 AM.

We did make a few changes on Tuesday. More and more, it looks
similar to Monday. Both the NAM and GFS have slowed the progression
of the next system moving in from the west. As a result, we have
removed the POPS from Tuesday night and also decreased sky cover for
many areas. We also lowered temperatures in the basins where
inversions will likely hold for another day. A gusty wind will also
develop across the southwestern Wind Corridor so Casper looks to
turn windy again. However, 700 millibar winds do not look strong
enough to support high winds at this time. It will also turn breezy
to windy in the Lee of the Absarokas. It is borderline for high wind
but we have time to watch it.

We also made some tweaks for Wednesday. Both the GFS and NAM show
the QPF from the approaching western system barely making it into
the west by Thursday morning. For now, we limited the POPS to slight
during the day and limited them to chance at night. We wanted to
half step in case of a model flip-flop. High wind may become more of
a concern this day with the GFS showing over 30 knots sustained at
Casper as the pressure gradient tightens. As for the chance the
inversions will finally break, it is a coin toss at this point. For
now, we kept temperatures below guidance.

.LONG TERM...Thursday through Monday

A weather system brings some snow to the west and southwest Thursday
and Thurs night. Southern WY should also see some light snow as
well. Not much snow expected east of the divide. On Friday
scattered light snow for most mountains with not much for the
lower elevations. On Saturday another weather system may spread
some light snow into the western zones with this light snow
continuing into Sat night. Again not much expected east of the
divide as the energy is weak by the time it gets there. Sunday
will be dry for most places. Scattered light snow to linger in the
western mountains mainly due to orographic lift. The models are
bringing additional moisture into the west and southwest for next
Monday. Will have a chance of light snow for these areas. Dry
weather east of the divide for now. Temps will be seasonal Thurs
with the mildest highs in the eastern zones. Slightly colder Fri
through Sunday. A tad milder next Monday in places. The strong
basin inversions should erode some or even break during this
period with cold air advection. However, any clear or partial
clear night will send low temps well below zero again in the
snow covered basins/valleys.

&&

.AVIATION.../12Z ISSUANCE/

Areas of fog/low stratus is expected Monday morning across SW
Wyoming, but is not expected to be as widespread or thick as the
past couple of days. KRKS terminal will have the best chance of
being impact by this fog/stratus. Patchy fog is expected elsewhere
across central and western basins and valleys. Have gone with
persistence and have prevailed IFR conditions in fog for the RIW
terminal. Winds will be light to very light today, but will begin to
increase somewhat Monday night in SE Fremont County into Natrona
County, Dubois area, Absaroka and portions of the Cody Foothills as
a weak lee trough develops.

&&

.FIRE WEATHER...

Fire Danger low for all of WY today. Cold seasonal temperatures,
good existing snow pack, and relatively light to moderate winds
will characterize today. Smoke dispersion will also remain poor
for all locations through the weekend with inversions in the
basins and valleys. Mixing may improve a bit on Tuesday in the
normally windier areas. Any chance of significant rain or snow
looks to hold off until at least Thursday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Dense Fog Advisory until noon MST today for WYZ028>030.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...WM
FIRE WEATHER...Hattings



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