Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180457
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1057 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 06Z TAFS through 06Z Thursday night)
Issued at 1056 PM MDT Wed May 17 2017

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

An upper level low pressure system over the northern Great Basin
will continue to slowly drift south across eastern Utah through
Thursday.  A dry slot over much of western Wyoming late Wednesday
evening will fill in with scattered to numerous snow showers from
the north and east 9z-15z from KJAC south to KPNA and KBPI.
Downslope northeast winds will then intensify with decreasing snow
showers vicinity and north of a KAFO-KBPI line Thursday afternoon
and evening.  Further south, a north to northeast wind will bring
widespread MVFR, areas of IFR snow and blowing snow vicinity and and
east of a KRKS-KLND line 12z-15z Thursday, pushing further west
along the Interstate corridor through the late morning and
continuing through Thursday evening.

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

An upper level low pressure system over the northern Great Basin
will continue to slowly drift south across eastern Utah through
Thursday. Rain and snow along with MVFR/IFR conditions will become
widespread across the area 12z-15z Thursday, with northeast surface
winds increasing to 15-25 knots across much of the area by Thursday
afternoon.  These conditions are expected to persist through
Thursday evening with gradual improvement from the west after 09z
Friday.

&&

.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 until 6 AM MDT Friday for WYZ015-019-022.

Flood Watch through late Thursday night for WYZ010-011.

Winter Weather Advisory until 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...Meunier
FIRE WEATHER...Baker



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