Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 191938

Area Forecast Discussion
National Weather Service Riverton WY
1238 PM MST Thu Jan 19 2017

.SHORT TERM...Tonight through Sunday

Light snow continues to move across NW portions this afternoon, as
clouds move in from the south and stay confined west of the
Divide. A 1018mb high remains centered near Vernal UT, while a
997mb leeside low is situated over NE WY. Expect this pressure
gradient to weaken this evening, as a weak cold front (boundary)
enters western portions. Light snow should also begin to fill in
across the rest of areas west of the Divide as it approaches.

Split flow of the jet emerging as the current storm system slowly makes
its way over the Pacific Northwest. A stronger branch (southern)
of the PFJ is supporting the next system over the east-central
Pacific and beginning to dig the base of the current trough. This
trough will become negatively-tilted tonight into Friday. At the
same time, the jet support of this system will separate from the
main flow and retreat northward into central Canada. The right
entrance region of this jet will be the main lifting mechanism for
the snow expected tonight and Friday east of the Divide. Sub-
advisory amounts are still expected for northern portions, with 1
to 3 inches in the Big Horn Basin and 3 to 5 inches in the Bighorn
Mountains and portions of the Absarokas and Owl Creeks/Bridger
Mountains. Other areas east of the Divide can receive a half inch
up to 2 inches.

Snow showers will linger across the far west Saturday and Sunday.
The PFJ will dig into the Desert Southwest on Saturday, before the
eastern Pacific low digs and builds a transitory ridge over the
Great Basin. Minor shortwaves from this low will rotate over the
Great Basin and produce these snow showers and Saturday. By Sunday,
Pacific moisture will be pulled in along the PFJ as the ridge axis
centers over the Rockies. This will start the upslope flow over
the western mountains and continue into the extended period.

.LONG TERM...Sunday night through Thursday

Areas of snow will spread across the west and southwest with
increasing clouds east of the Continental Divide with windy
areas along and east of the east slopes of the mountains and through
the wind corridor. Snow will spread east across the area Monday and
Monday night with colder temperatures most areas.  Tuesday will see
snowfall decrease from west to east with partial clearing possible
in the west.  Temperatures will continue to fall.  Some snow will
linger in the mountains and east Tuesday night with clearing west
and central allowing for continued cooling.  Some light snow showers
may linger over the mountains Wednesday but the general trend will
be for cooling and clearing.  This trend for dry and clearing
conditions will continue Wednesday night and Thursday additional
cooling is not expected.



MVFR to IFR ceilings and visibilities reduced in snow and fog are
expected to overspread the far west spreading into the Upper Green
River Basin and Sweetwater County during the early evening. The KJAC
terminal should be most impacted by this system with a prolonged
period of IFR conditions expected. Farther southeast, confidence
decreases, but will still prevail MVFR, occasional IFR, conditions
at area terminals will continue into Friday afternoon most areas.
Mountains will already be obscured and remain obscured through
the taf period. Winds are expected to be mainly light in most


A low pressure trough pushing across the region will result in areas
of MVFR to IFR ceilings and visibilities reduced in snow and fog.
Light snow breaking out especially over northern and central
Wyoming and becoming widespread 06Z - 09Z. All terminals expected
to be impacted tonight and Friday into the afternoon. Mountains
are expected to be obscured this evening and remain so through



Fire Danger low for all of WY through the weekend. Cold seasonal
temperatures and a good existing snow pack will continue. Light
snow will continue across NW portions, filling in over areas west
of the Divide this evening. Light to moderate snow showers are
expected east of the Divide later tonight and Friday. Gusty
southwest winds across the Cody Foothills will be ending later
this afternoon and then over the Wind Corridor later tonight.
Smoke dispersion will remain poor east of the Divide through
Friday morning before seeing improvement...while west of the
Divide will see better smoke dispersal by this afternoon.



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