Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230850
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
150 AM MST Thu Feb 23 2017

.SHORT TERM...Today through Saturday night

Bands of snow continue to fill in over Natrona and Fremont counties,
while steady bands of snow fall across Sweetwater and southern
Lincoln counties. Cloud tops have rapidly cooled since 00Z and range
between -40 & -50C. The upper low continues its eastward trek this
evening, currently over NE NV/NW UT. Based on sat analysis, a triple
point low should be located somewhere near SLC. This sfc low is
progged to quickly move across Uinta and Sweetwater counties tonight
and be near RKS by 12Z Thursday. The low will then move toward NE
Sweetwater County, before slowly moving into western Carbon County
tonight. The low will bottom out ~1000mb between 12Z and 18Z. Winds
across the Wind Corridor, South Pass, the Wind River Mountains and
Sweetwater County will quickly increase as a result. Increased winds
in these areas slightly, with 60-70 mph over South Pass, the west
slopes of the Wind Rivers and the Upper Green River Basin Foothills.
Winds of 35-50 mph will also be widespread east of the Divide
through 00Z Friday. The heaviest areas of snow today will be over SW
Natrona/SE Fremont counties and the east slopes of the Wind River
Mountains. Snowfall totals in these areas will be 10 to 14 inches,
minus any accumulations from Wednesday night. Decreased amounts over
Casper, as sfc winds will be out of the east-northeast. This is not
the most conducive direction for significant snow accumulation.
Also, models are signaling snow bands under the deformation axis to
form north of the city. Thus, 10 to 12 inches are now expected from
northern Natrona to SW portions.

As the sfc low exits the area, the forecast area will be under the
mean trough axis. There will not be any upper level support for
continued moderate or heavy snow Thursday night through Friday
night. The upper level low supporting the front will gradually exit
the state Thursday night. This, along with other minor embedded
shortwaves, will keep light snow continuing Friday. Accumulations
are expected to remain light. Winds will also quickly subside
between 00Z and 06Z Friday, with light winds expected across the
forecast area by 12Z. Precipitation will end across the area, from
south to north late Friday afternoon and through the overnight
hours, as a shortwave ridge builds over the region.

.LONG TERM...Sunday through Thursday

Sunday looks to be mainly dry with perhaps some light snow over
the far west, ahead of trough digging southeast into the Pacific
Northwest. This trough is expected to push into the Intermountain
West Sunday night, and then across the Rockies Monday and Tuesday
with a couple of waves in the mean longwave trough impacting the
area. A decent shot of snowfall across the west beginning Sunday
night, and continuing at times through Monday night/Tuesday. East
of the Divide will remain mainly dry until the main trough/cold
front push across the area late Monday into Tuesday time frame.
The main impact looks to be across the far west where some
significant snowfall could occur Monday. Also breezy to windy
conditions are expected with this trough. Although high wind
potential does exist, models have trended weaker with the wind
fields, and surface pressure gradients.

In wake of this trough, northwest flow is expected Wednesday and
Thursday. Enough moisture in the flow for slight to chance PoPs
across the northwest. Otherwise, mainly dry and cool.

Temperatures in the long term are expected to be 10 to 20 degrees
below average.

&&

.AVIATION.../12Z ISSUANCE/

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

A low pressure system will move east across southern Wyoming this
morning and out into the Central Plains Thursday afternoon. The
main impacts with this storm will be across southwest Wyoming, or
from approximately 40SM north of KRKS and southward, where
widespread IFR/LIFR conditions and higher terrain obscurations are
expected through Thursday afternoon. Downslope northeast winds
will limit snow showers across most of northwest Wyoming including
vicinity KJAC and KPNA, where occasional MVFR/IFR shsn may occur,
but VFR conditions are expected to prevail. The flow will become
more westerly early Friday morning, when snow showers are expected
to become more numerous vicinity KJAC and KPNA.

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

A low pressure system will move east across southern Wyoming this
morning and into the Central Plains Thursday afternoon. This
system will bring widespread IFR conditions, areas of LIFR
conditions, in moderate to locally heavy snow, and mountain
obscurations across most areas. Areas of blizzard conditions with
NNE winds 30-40kts will occur from around 12z to 21z Thursday
south of a KCPR-KLND line. KWRL-KPOY routes will be least affected
with primarily MVFR, occasional IFR conditions through the day
Thursday. Conditions will gradually improve Thursday evening, as
the low moves away across the Central Plains with decreasing winds
and snow tapering off. However, widespread MVFR/IFR conditions
and mountain obscurations are expected to linger through 12z
Friday.

&&

.FIRE WEATHER...

A significant winter storm will continue to impact much of Central
and Western Wyoming today with areas of moderate to heavy snow.
Light snow will linger this afternoon and through the day Friday,
before ending Friday evening. Strong northerly winds will occur with
this snow Thursday, over the Wind River Mountains, southeastern
Fremont and eastern Sweetwater counties. Light to moderate snow will
also occur west of the Divide during this time, ending from south to
north Friday evening.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Blizzard Warning until 11 AM MST Friday for WYZ014-015-019-030.

Winter Storm Warning until 11 AM MST Friday for WYZ007-017-018-
020-022-028-029.

Winter Storm Warning from 5 AM early this morning to 11 AM MST
Friday for WYZ010-011.

Winter Weather Advisory from 5 AM early this morning to 11 AM
MST Friday for WYZ003-005-009.

&&

$$

SHORT TERM...LaVoie
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...LaVoie


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