Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 040631 AAA
AFDRIW

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1131 PM MST Sat Dec 3 2016

.UPDATE...Added 06z aviation discussion.

&&

.AVIATION.../06Z ISSUANCE/

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

Winds aloft will increase ahead of an approaching trough/cold front
Sunday morning with areas of LLWS developing 15z-18z.   Surface
southwest wind at 20-30 kt with gusts 40-45 kt will prevail from
South Pass-50SM NE KRKS-KCPR 12z Sunday-06z Monday.

Also, peaks above 9kft along the Continental Divide will be mostly
obscured in -sn 12z Sunday - 12z Monday.

A cold front will plunge south through KCOD-KBYG around 08z Monday
and to near a KRIW-KCPR line by 12z Monday.  Areas of MVFR/IFR -sn
and gusty north wind will follow the cold front.


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

Snow, widespread IFR conditions and mountain obscurations will
increase from north to south, to a vicinity and north of a KAFO-KDUB
line by 12z Sunday.  Ridgetop winds will also increase with LLWS
becoming widespread by 17z across the area.

IFR conditions will prevail vicinity and north of a KAFO-KPNA line
through 06z Monday, with a cold front driving areas snow further
south and east along the Interstate 80 corridor 06z-12z Monday.

LLWS will subside behind a cold frontal passage with precipitation
becoming more showery along with some improvement in ceilings and
visibility vicinity and north of a KJAC-KDUB line by 12z Monday.

&&

.PREV DISCUSSION... /issued 131 PM MST Sat Dec 3 2016/

Short Term...Tonight Through Sunday

Areas of strong winds will continue along the east slopes of the
Absaroka and Wind River mountains...the Cody Foothills and the
upper Wind River basin around Dubois. Also strong winds will blow
through the wind corridor across eastern Sweetwater...southern
Fremont and Natrona counties. The windy areas will see significant
warming. Snow will increase across the western mountains and
valleys towards sunrise Sunday with periods of moderate to heavy
snow expected in the Tetons and southern Mountains in Yellowstone
National Park where a Winter Storm Warning is in effect. Snow
will spread into the Wyoming and Salt River ranges...and the wind
River and Absaroka mountains where Winter Weather Advisories have
been issued..

Long Term...Sunday Night Through Saturday

Snow is expected to be moderate to heavy at times over most of
the west with strong west to southwest winds.  Up to 20 inches
of snow is possible in and around the Teton Mountains with up to
a foot of snow in the Wyoming and Salt River Ranges...and the
Absaroka and Wind River mountains. Snow is expected to taper off
in the west and spread into the east Monday. Snowfall in the east
is expected to be light and spotty while local areas with north
and east facing slopes may see up to 5 inches of snow.
Temperatures will turn much colder as this storm system exits to
the east of the area bringing cold air in behind it. Cold
temperatures especially in the valleys and Basins should remain
with little mixing to scour the dense air out. Much of the week
will see lows dipping below zero at night and highs in the 20s.
The east will warm first across eastern Johnson and Natrona
counties that lack barriers to mixing. Some snow will return to
the west Thursday afternoon increasing Thursday night and Friday.
East of the Continental Divide winds will increase along the east
slopes of the Absaroka and Wind River mountains...the Cody
Foothills and the upper Wind River basin around Dubois. Also winds
will blow through the wind corridor across eastern
Sweetwater...southern Fremont and Natrona counties. The windy
areas will see significant warming Thursday and Friday. Friday
night another cold front will sweep south across the area with
snow spreading east of the Continental Divide and colder air
returning for Saturday.

Aviation.../00Z Issuance/

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

Mid to high level clouds remain well to the east, except over the
Bighorn Mountains. VFR and dry conditions are expected tonight into
Sunday.  Mid to high level clouds will move back over the area
tonight after midnight. Windy westerly surface flow will occur in
the wind corridor of SE Fremont into Natrona County as well as along
the Cody Foothills, around Dubois area and the Wind River Basin
near KRIW.

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

The far western valleys will be impacted by persistent MVFR ceilings
and/or Visibilities in light snow this afternoon, possibly improving
to low MVFR conditions early tonight as the coverage of light snow
decreases. Mountains across the far west will be obscured much if
not all of the time with LIFR conditions over mountain passes.
Farther east/southeast into the Upper Green River Basin into
Sweetwater County, little or snowfall is expected with mid/high
level cloudiness.

Fire Weather...

Areas of strong winds will continue along the east slopes of the
Absaroka and Wind River mountains...the Cody Foothills and the
upper Wind River basin around Dubois. Also strong winds will blow
through the wind corridor across eastern Sweetwater...southern
Fremont and Natrona counties. The windy areas will see significant
warming. Snow will increase across the western mountains and
valleys towards sunrise Sunday with periods of moderate to heavy
snow expected in the Tetons and southern Mountains in Yellowstone
National Park where a Winter Storm Warning is in effect. Snow
will spread into the Wyoming and Salt River ranges...and the wind
River and Absaroka mountains where Winter Weather Advisories have
been issued. With low clouds and snow...Mixing heights will be
quite low with little mixing resulting in generally poor smoke
dispersal across the west. Windy areas East of the continental
divide will have good afternoon smoke dispersal Sunday but poor
smoke dispersal on Monday with areas of snow and colder
temperatures moving in across the area.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM Sunday to noon MST Monday for
WYZ002-014-015-023>025.

Winter Storm Warning from 5 AM Sunday to noon MST Monday for
WYZ001-012-013.

&&

$$

SHORT TERM...C.Baker
LONG TERM...C.Baker
AVIATION...AEM
FIRE WEATHER...C.Baker


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