Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 160601
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1101 PM MST Mon Jan 15 2018

.SHORT TERM...This evening through Thursday
Issued at 130 PM MST Mon Jan 15 2018

A cold Canadian air mass has moved in across the area
leaving areas of low stratus and fog in the valleys and basins
today.  Some light snow fell but is over now.  Temperatures
will be difficult with the dense stratus insulating some areas
while clearing mainly in the north and east will result in
below zero lows tonight mainly from -5 to -10.  The stratus
and fog will be slow to dissipate on Tuesday and may linger
in the valleys and basins longer than now expected with rather
light wind aloft as high pressure will dominate.  Some warming
will occur especially east of the Bighorn mountains where rapid
warming may occur.  The models are less bullish on precipitation
moving into the west mid week compared to the past few days.
now Thursday looks to be the arrival time oh scattered mountain
snow with warming east of the Continental Divide.

.LONG TERM...Thursday night through Monday night
Issued at 130 PM MST Mon Jan 15 2018

Models continue to trend toward a warm, southwest flow regime over
the forecast area Thursday evening into Friday, as a longwave trough
makes its way onshore over the PACNW. PoPs will steadily increase
across the NW Thursday night, with low snow ratios and valley rain
(or rain/snow mix) initially. Temperatures will finally begin to
decrease after 12Z Friday, as the associated cold front makes its
way toward the SE. As it does so, chances for precipitation will
increase east of the Divide. These chances will be widespread, with
lower elevations remaining rain or a rain/snow mix. Temperatures in
these areas will remain relatively warm ahead of the front, changing
over to snow by 00Z Saturday. Models also continue to prog this
system diving south over the Four Corners, with some energy
splitting over WY by 00Z Saturday. A slight chance for snow will
continue Saturday, but most of the focus will shift to the east,
with the best chances for snow possibly continuing over Natrona and
eastern Sweetwater counties. With lingering snow showers possible
Saturday night, the focus will return to the west Sunday and Monday.
The pattern will quickly reset, as another storm system quickly
follows on the heels of the Friday system. Associated moisture from
this system will again impact western portions, but at this point
only looks like isolated to scattered chances for snow. Apart from
western portions, temperatures Friday will be slightly above normal.
Otherwise, readings through the forecast period look to be at or
slightly below normal.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1057 PM MST Mon Jan 15 2018

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

Satellite fog imagery showed the northern extent of a fog bank
near KJAC with some continuing erosion around the edges. Any
improvement is expected to be temporary early Tuesday morning with
steep inversions remaining over the area. Thus, forecasting LIFR
conditions to persist into Tuesday afternoon. An extensive area of
MVFR ceilings around FL090 will likewise persist across the Upper
Green River Basin (KBPI, KPNA) through around 18z Tuesday with
possibly some improvement along the west slopes of the Wind River
Range, vicinity KPNA, a few hours earlier. Once fog and low clouds
lift in the afternoon, a weak upper level disturbance and some
mid-level clouds should hinder the redevelopment of fog and lower
ceilings through 12z Wednesday.

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

Satellite fog imagery showed a persistent area of MVFR ceilings
across  the Wind River Basin. Lower IFR ceilings along the Cody
Foothills, KCOD, showed signs of erosion over the last few hours.
KCOD is expected to scatter out by 12z, while the larger area of
MVFR ceiling over KRIW and KLND will likely persist through at
least 16z Tuesday. Once these ceilings dissipate by early Tuesday
afternoon, VFR conditions with unlimited ceilings are expected to
prevail through 12z Wednesday. Fog, low cloud redevelopment should
be hindered as a weak upper level disturbance moves across the
area.

&&

.FIRE WEATHER...
Issued AT 130 PM MST Mon Jan 15 2018

A cold Canadian air mass has moved in across the area
leaving areas of low stratus and fog in the valleys and basins
today.  Some light snow fell but is over now.  Temperatures
will be difficult with the dense stratus insulating some areas
while clearing mainly in the north and east will result in
below zero lows tonight mainly from -5 to -10.  The stratus
and fog will be slow to dissipate on Tuesday and may linger
in the valleys and basins longer than now expected with rather
light wind aloft as high pressure will dominate.  Some warming
will occur especially east of the Bighorn mountains where rapid
warming may occur.  The models are less bullish on precipitation
moving into the west mid week compared to the past few days.
now Thursday looks to be the arrival time oh scattered mountain
snow with warming east of the Continental Divide.  Inversions
will be in place over the cold valleys and basins with light wind
resulting in generally poor smoke dispersal through Wednesday.

&&

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

$$

SHORT TERM...Baker
LONG TERM...LaVoie
AVIATION...Meunier
FIRE WEATHER...Baker



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