Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 010608
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1108 PM MST Tue Feb 28 2017

.Short Term...Tonight Through Friday

Rather strong west flow aloft will continue to bring in mid and
low level moisture with widespread light snow over the west
tonight through Wednesday night. Snowfall accumulations will
remain light with 3 to 6 inches over 24 hours continuing. Locally
higher amounts will be possible in the Tetons and southern
Yellowstone National Park. The strong winds aloft will combine
with a strong surface pressure gradient in the north to produce
high winds in the Lower east slopes of the Absaroka mountains
and the Cody foothills from midnight tonight through midnight
Wednesday night.  Little if any precipitation will make it east
of the mountains. Areas of blowing and drifting snow will be
prevalent with the strong ridgetop and pass level winds. Thursday
the moisture will decrease and snowfall will taper off or end from
south to north continuing to dry out Thursday night and Friday.
Temperatures will slowly warm through Friday.

.Long Term...Friday Night Through Tuesday

Weak ridging/upper level NW flow will flatten with the axis pushed
east into the Plains in response to an approaching embedded upper
level SW trough/jet streak that will arrive near western WY late
Friday night/early Saturday morning. The transition to
flat/southwesterly flow on Friday will allow for periods of stronger
lee side troughing and gusty wind potential. Some of these winds
will border on `High` periodically across the usual suspect areas
(lee side foothills east of the Continental Divide and across the
Wind Corridor) through most of the forecast...especially Sunday
afternoon into Monday morning and possibly again from Monday night
through Tuesday morning. Temperatures will also respond positively
to the lee side troughing/windy set-up east of the Divide with near
to slightly above normal temperatures through at least Monday.
Possible seasonally strong cold front may swing through in the
Monday/Tuesday timeframe putting the brakes on warming (and
melting?). Additionally, light areas of snowfall across the west
will increase some, both in intensity and extent, Saturday morning
along with the arrival of the jet...especially over the northwestern
mountains where the moisture will be. If position and timing of this
system remain on track, some highlights will be needed from Saturday
night onward for at least Teton and Park counties.

&&

.Aviation.../06Z Issuance/

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

The snowfall today is expected to be more stratiform, lighter, and
more confined to the mountains than what has occurred over the past
couple of days. The KJAC terminal should see persistent ceilings
between 025-050 kft agl with flurries at times. Breezy southerly
winds could also cause some BLSN at the airport. In the Upper Green
River Basin (KBPI and KPNA), there will be patchy fog this morning
with a stratocu deck forming by midday if not a bit sooner with some
flurries possible. Across the far south including KRKS, windy west
winds will be the main issue, but cannot rule out near MVFR ceilings
at times. Far western mountain will be obscured much of the time
with MVFR/IFR conditions through the period.

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

Snow and associated MVFR/IFR conditions over the Bighorn Mountains
and the lower elevations of Johnson County will push away from the
area by around 09Z. The strong northwest around KBYG will also
gradually subside by sunrise. Otherwise, windy west to southwest
wind, and low level wind shear at times will be the main concern
today. Interior parts of the basins are expected to see much lighter
winds. Tonight, a cold front will approach from the north. This
combined with a moist northwest flow could result in some snow
shower activity across the far north especially over the Bighorn
Mountains after 00Z Thursday. Also, breezy northwest winds are
expected to develop at KBYG tonight between 03Z and 06Z.

Please see the Aviation Weather Center for the latest information on
icing and turbulence forecasts.

&&

.Fire Weather...

Rather strong west flow aloft will continue to bring in mid and
low level moisture with widespread light snow over the west
tonight through Wednesday night. Snowfall accumulations will
remain light with 3 to 6 inches over 24 hours continuing. Locally
higher amounts will be possible in the Tetons and southern
Yellowstone National Park. The strong winds aloft will combine
with a strong surface pressure gradient in the north to produce
high winds in the Lower east slopes of the Absaroka mountains
and the Cody foothills from midnight tonight through midnight
Wednesday night.  Little if any precipitation will make it east
of the mountains. Areas of blowing and drifting snow will be
prevalent with the strong ridgetop and pass level winds. Thursday
the moisture will decrease and snowfall will taper off or end from
south to north continuing to dry out Thursday night and Friday.
Temperatures will slowly warm through Friday. Poor smoke dispersal
is expected through Friday in the valleys. The windy areas over
and near the mountains and through the wind corridor may
experience fair to good smoke dispersal in the afternoons through
Friday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from midnight tonight to midnight MST
Wednesday night for WYZ002-003.

&&

$$

SHORT TERM...C.Baker
LONG TERM...Braun
AVIATION...WM
FIRE WEATHER...C.Baker


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