Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 130548
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1048 PM MST Fri Jan 12 2018

.UPDATE...
Issued at 508 PM MST Fri Jan 12 2018

Winter storm warnings and winter weather advisories have expired
across western Wyoming. Additional accumulations have been light
since sunrise today, mostly around an inch or less with up to 3
inches in the mountains.

&&

.SHORT TERM...(This evening through Monday)
Issued at 118 PM MST Fri Jan 12 2018

Cold north northwest flow behind the main low
pressure trough will keep areas of light snow in the
north and west, mainly in the mountains tonight.
Temperatures will generally cool especially in the north.
Some light snow will linger over the northwest through
Sunday with partial clearing.  Monday the first wave
of colder modified Arctic air will bring light snow
to the north and east with temperatures falling across
the area.  Snowfall is expected to be light with the
best accumulations in the northern Bighorn mountains
and Northern Absaroka mountains.


.LONG TERM...(Monday night through Friday)
Issued at 118 PM MST Fri Jan 12 2018

Overall, the MR models with respect to the extended forecast are in
fair agreement through the forecast period - with a few low impact
differences. After an Arctic cold front does its business Monday,
leaving clearing/cold skies/atmosphere in its wake, shortwave
ridging immediately begins Tuesday. While Tuesday morning
temperatures have been lowered some over those given (and compared
to our eastern neighbors a bit), the strength of the front and later
proximity to a post frontal 1050 mb high over the northern/high
Plains will likely clear skies and allow for even colder morning
temperatures than are currently in place. This will probably be a
daily chore over the next few days. As the shortwave ridge
translates through WY Tuesday and part of Wednesday, a shortwave
trof follows it into wrn WY with EPAC moisture and precipitation
chances increasing west of the Divide. Another small difference
between models that may mean something later on arises with this
trof as the EC slows and plunges a bit further south and pinches off
a closed low in the process produces. This would allow for higher
QPF across the southwestern FA (EC) while the slightly faster GFS
keeps the system split to some extent with the wetter portion racing
off in the northern stream while the southern portion gets ripped up
and disappears over the CO mountains. Differences ATtM are minimal.
Then, the models return to some common symmetry with respect to time
and place with another period of brief ridging taking place on
Thursday. The slightly faster GFS then follows the passing ridge,
under transitioning southwest flow, with renewed EPAC moisture and
precip chances go up about 6 to 8 hrs ahead of the EC. Timing
differences aside (not bad for 7-8 days out), the EC is probably
more bullish with respect to moisture and the location of the mean
trof position. The GFS expresses better the pattern(s) the FA has
been seeing lately while the EC seems slightly anomalous and heavy
handed. One thing is for sure, none of this really matters in an
absolute sense and will likely change face several times over the
next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1047 PM MST Fri Jan 12 2018

West of the Continental Divide...KJAC, KBPI, KPNA and KRKS

Higher mountains will remain mostly obscured through the morning
with local MVFR ceilings and visibilities in -SN vicinity KJAC and
KPNA. Some clearing will occur Saturday afternoon with
obscurations mainly over the higher peaks. Areas of IFR/MVFR
ceilings will likely seep in from eastern Idaho to vicinity KJAC-
KAFO overnight Saturday night.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

Northwest flow will keep some areas of MVFR -SN vicinity and north
of a KPOY-KBYG line through Saturday morning, with the Bighorn
range and northern Absaroka range remaining mostly obscured. VFR
conditions are expected to prevail Saturday afternoon through
Saturday night; patchy fog in the lower basins may partially
obscure terrain vicinity KWRL and KRIW after 06z Sunday.

&&

.FIRE WEATHER...
Issued AT 118 PM MST Fri Jan 12 2018

Cold north northwest flow behind the main low
pressure trough will keep areas of light snow in the
north and west, mainly in the mountains tonight.
Temperatures will generally cool especially in the north.
Some light snow will linger over the northwest through
Sunday with partial clearing.  Monday the first wave
of colder modified Arctic air will bring light snow
to the north and east with temperatures falling across
the area.  Snowfall is expected to be light with the
best accumulations in the northern Bighorn mountains
and Northern Absaroka mountains.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Meunier
SHORT TERM...Baker
LONG TERM...Braun
AVIATION...Meunier
FIRE WEATHER...Baker


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