Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 152046
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
146 PM MST Fri Dec 15 2017

.SHORT TERM...This evening through Monday
Issued at 145 PM MST Fri Dec 15 2017

...Snow in the western mountains tonight, spreading east
Saturday and Saturday night...

A Pacific low pressure trough moving south and east from British
Columbia and the Pacific northwest will spread snow into the western
mountains late this evening.  The heaviest snow is expected in the
Tetons.  East of the Continental Divide windy areas are expected along
and near the east slopes of the mountains as clouds spread east combining
for warmer low temperatures.  Snow will continue across the western
mountains through Saturday.  The trough and a Canadian cold front will
move into the north along and east of the Continental Divide by early
morning with snow and areas of blowing snow spreading south into central
and east central Wyoming through the morning Saturday. Snow will continue
Saturday night tapering off late. Temperatures will cool significantly
Sunday and Monday.  Clearing will occur Sunday and Sunday night with some
fog possible in the valleys.  A weaker Pacific trough will bring areas
of snow to the northwest and west on Monday.  Windy areas will again
develop along and near the east slopes of the mountains with warming in
the foothills.

.LONG TERM...Monday night through Friday
Issued at 145 PM MST Fri Dec 15 2017

Starting Monday night a broad and relatively flat ridge will set up
just off the coast of CA. This will allow for the propagation of a
few shortwaves into the WY area Tuesday through Wednesday morning.
Precip will focus mainly in the Northwest Mountains and Valleys and
should be fairly light. The door will remain open low pressure
system to move in Wednesday night. This system is very similar to
the one expected this Saturday but may have a bit more cold air
behind it.  Snow looks to last most of the day on Thursday. GFS and
ECMWF indicate a cut off low forming over UT Thursday afternoon
which could increase snow totals for the southern and central areas.
On Friday the Pacific High builds much further north shifting the
flow over WY almost directly from the north.  This could push our
temperatures into the single digits and possibly lows below zero.
Models are still conflicting on how cold with 700mb temps between
-15 and -24, but all are trending towards much colder air Friday.

&&

.AVIATION...For the 00Z TAFS through 00Z Saturday evening
Issued at 145 PM MST Fri Dec 15 2017

VFR predominant across the area the rest of the day through late
tonight. Winds will continue to be gusty at KCOD until late evening
and KCPR until early tomorrow morning. The next frontal system will
enter the area overnight, bringing snow showers and MVFR/IFR
conditions across the area. The Western Mountains and Valleys will
start around 08Z Saturday morning, including KJAC, and spread east
and south.  By 14Z all terminals will be in MVFR to IFR conditions
lasting the rest of the period. West of the divide, accumulations
will be around 1-3 inches. East of the divide, accumulations will be
2-4 inches with KCPR seeing 3-6 inches.

&&

.FIRE WEATHER...
Issued AT 145 PM MST Fri Dec 15 2017

A Pacific low pressure trough moving south and east from British
Columbia and the Pacific northwest will spread snow into the western
mountains late this evening.  The heaviest snow is expected in the
Tetons.  East of the Continental Divide windy areas are expected along
and near the east slopes of the mountains as clouds spread east combining
for warmer low temperatures.  Snow will continue across the western
mountains through Saturday.  The trough and a Canadian cold front will
move into the north along and east of the Continental Divide by early
morning with snow and areas of blowing snow spreading south into central
and east central Wyoming through the morning Saturday. Snow will continue
Saturday night tapering off late. Temperatures will cool significantly
Sunday and Monday.  Clearing will occur Sunday and Sunday night with some
fog possible in the valleys.  A weaker Pacific trough will bring areas
of snow to the northwest and west on Monday.  Windy areas will again develop
along and near the east slopes of the mountains with warming in the
foothills.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM Saturday to 5 AM MST Sunday
for WYZ002-003-005-007>011-014-015-017>020-022-025.

Winter Weather Advisory from 11 PM this evening to 5 PM MST
Saturday for WYZ012.

High Wind Warning until 6 PM MST this evening for WYZ003.

&&

$$

SHORT TERM...Baker
LONG TERM...Hulme
AVIATION...Hulme
FIRE WEATHER...Baker



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