Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 180006 AAA
AFDRIW

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
606 PM MDT Wed May 17 2017

.UPDATE...
Issued at 604 PM MDT Wed May 17 2017

Allowed Winter Weather Advisories to expire in the Teton, Gros
Ventre, Salt and Wyoming Ranges; where dry air as prevailed on
east side of upper low over southeast Idaho early this evening.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 140 PM MDT Wed May 17 2017

A large upper level low pressure Pacific storm system over
southern Idaho and northern Utah will dig south and east into
western Colorado Thursday and Thursday night bringing significant
Pacific moisture and cold air to the region. This is a very
difficult storm to forecast snow accumulations as the snow level
will fluctuate from the foothills to the lower valley elevations
at night and rise again during the day. Mountain snowfall most
certain while lower elevation amounts very questionable. Have
issued winter weather advisories for eastern Johnson, Natrona,
Fremont and eastern Sweetwater counties from later tonight, 3 am
through 6 am Friday morning. Snow will likely change to rain at
times but heavy snow may significantly impact visibility and
driving conditions. Temperatures consistently colder over the
past 24 hours. Worst case is colder and all snow which could
produce a foot to a foot and a half snowfall around Casper,
Riverton and Lander. Best case all rain but too cold for mountain
snow melt which would reduce flooding potential. Models keep more
precipitation through Friday now but air will be rather cold
limiting amounts. Slow clearing and warming on Saturday.

.LONG TERM...(Saturday night through Wednesday)
Issued at 140 PM MDT Wed May 17 2017

Unsettled nw (becoming n) flow through the period with multiple sewd
moving weather systems to deal with. The first one looks to move
from ID across srn WY and nrn CO Saturday night into Sunday with
considerable mountain rain/snow and a chance of lower elevation rain
showers. Another quick moving system drops right behind this one
Sunday night to keep in unsettled in advance of a stronger swd
moving system moving out of Canada. This one looks to pack more
of a punch for the north and east with a good frontal passage with
widespread mountain snow (possibly heavy in the Big Horns and
Beartooth Plateau) and a good chance of mostly rain showers across
the lower elevations with falling snow levels into the foothills
later Monday into Tuesday. One more system is expected to drop
straight south on Wednesday to keep the area unsettled and cool
with a chance of showers and higher elevation snow.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 140 PM MDT Wed May 17 2017

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS Terminals

Widespread snow over northwest WY through 06Z Thursday, before
drying moves into that location. The rest of the region will see
isolated to scattered rain or snow showers through Thursday.
Mountains will be obscured in NW WY through the period. Windy
conditions will be common today in southwest WY through 00Z, then
decreasing. Please see terminal forecasts for details.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL Terminals

Showers will become more numerous over northern WY this afternoon
with widespread rain through 18Z Thursday. Then drying will move
into this area after 18Z Thurs. Some areas above 5K feet will change
to or mix with snow like KCOD after 12z Thu. Expect areas of
MVFR/IFR conditions over the north through Thursday. Windy
conditions will occur in the central part of WY today with the wind
decreasing after 00Z. Widespread MVFR to IFR cigs/vsbys will move
into the rest of central WY after 09-12z Thu and continue all day
with widespread rain and snow. Please see terminal forecasts for
details.


&&

.FIRE WEATHER...
Issued AT 140 PM MDT Wed May 17 2017

A large upper level low pressure Pacific storm system over
southern Idaho and northern Utah will dig south and east into
western Colorado Thursday and Thursday night bringing significant
Pacific moisture and cold air to the region. This is a very
difficult storm to forecast snow accumulations as the snow level
will fluctuate from the foothills to the lower valley elevations
at night and rise again during the day. Mountain snowfall most
certain while lower elevation amounts very questionable. Have
issued winter weather advisories for eastern Johnson, Natrona,
Fremont and eastern Sweetwater counties from later tonight, 3 am
through 6 am Friday morning. Snow will likely change to rain at
times but heavy snow may significantly impact visibility and
driving conditions. Temperatures consistently colder over the
past 24 hours. Worst case is colder and all snow which could
produce a foot to a foot and a half snowfall around Casper,
Riverton and Lander. Best case all rain but too cold for mountain
snow melt which would reduce flooding potential. Models keep more
precipitation through Friday now but air will be rather cold
limiting amounts. Slow clearing and warming on Saturday. With
widespread cold clouds and precipitation, mixing heights will be
low with poor smoke dispersal through Friday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM Thursday to 6 AM MDT Friday
for WYZ007-017-018-030.

Winter Storm Warning from midnight tonight to 6 AM MDT Friday
for WYZ015-019-022.

Flood Watch through late Thursday night for WYZ010-011.

Winter Weather Advisory from midnight tonight to 6 AM MDT Friday
for WYZ010-011-020.

Winter Weather Advisory until 6 AM MDT Thursday for WYZ001.

Winter Storm Warning until 6 PM MDT Thursday for WYZ008-009.

Winter Weather Advisory until noon MDT Thursday for WYZ002.

&&

$$

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



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