Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 150628
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1128 PM MST Thu Dec 14 2017

.SHORT TERM...This evening through Sunday
Issued at 115 PM MST Thu Dec 14 2017

Tonight and Friday will be dry with areas of valley fog mainly
in the west. Clouds will increase in the northwest Friday afternoon
with strong winds along the east slopes of the Absaroka mountains
and Cody foothills.  A Pacific low pressure trough will move southeast
from British Columbia and the Pacific Northwest bringing snow and colder
temperatures to the western Mountains and valleys Friday night
with snow becoming widespread by late evening. The heaviest
snowfall will be in west central and northwest areas especially
before midnight with lighter amounts to the south in Lincoln and
Sublette counties.  Snowfall will spread east of the Continental Divide
late Friday night becoming more widespread by Saturday morning.   Snowfall
will continue in the west Saturday and spread into central and south areas
east of the Continental Divide with the heaviest snowfall in Natrona and
Fremont counties tapering off in the west Saturday evening and in the
east Sunday morning when colder Canadian air moves in with northerly
winds.

.LONG TERM...Sunday night through Thursday
Issued at 115 PM MST Thu Dec 14 2017

A weak transitional ridge will be in place Sunday night but will
move out of the area overnight allowing for a general NW upper level
flow.  This will set up a shortwave to arrive on Monday focusing
precip in the NW Mountains through much of Tuesday.  Wednesday the
low will arrive from the NW coast bringing widespread snow to WY.
Models are in a bit of disagreement at this point with GFS forming a
cut-off low over the SW US and ECMWF/Canadian deepening the trough
to our east.  The GFS and ECMWF are both leading to a direct north
flow Thursday which could lead to a very cold weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1127 PM MST Thu Dec 14 2017

West of the Continental Divide...KJAC, KPNA, KBPI, and KRKS

Areas of fog were beginning to push into northwest Wyoming (north of
Jackson Lake) from eastern Idaho late Friday evening.  A northerly
drainage flow may push some of this fog into vicinity KJAC by 12z
Saturday.  Fog will also likely continue to expand across the upper
Green River Basin, occasionally affecting KBPI and KPNA through the
morning.  VFR conditions will then prevail through Saturday evening
with increasing mid and high clouds.  A cold front will rapidly
spread increasing snow, mountain obscurations, and widespread
MVFR/IFR conditions NW to SE across the area 06z-12z Saturday.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

VFR conditions will prevail across the area through 06z Saturday.
Surface southwest winds will increase to 25-35G40-45kts vicinity
50SM NE KRKS-KCPR 16z-19z Friday, while areas of LLWS spread down
the east slopes of the Divide, vicinity KCOD-KDUB-KLND.  A cold
front will plunge south to vicinity KCOD-KBYG line around 06z
Saturday and to a vicinity KRIW-KCPR line by 12z Saturday.  Areas of
MVFR-IFR vsbys and cigs in -SN will spread in behind the front, most
higher mountains will be obscured by 12z Saturday.
&&

.FIRE WEATHER...
Issued AT 115 PM MST Thu Dec 14 2017

Tonight and Friday will be dry with areas of valley fog mainly
in the west. Clouds will increase in the northwest Friday afternoon
with strong winds along the east slopes of the Absaroka mountains
and Cody foothills.  A Pacific low pressure trough will move southeast
from British Columbia and the Pacific Northwest bringing snow and colder
temperatures to the western Mountains and valleys Friday night
with snow becoming widespread by late evening. The heaviest
snowfall will be in west central and northwest areas especially
before midnight with lighter amounts to the south in Lincoln and
Sublette counties.  Snowfall will spread east of the Continental Divide
late Friday night becoming more widespread by Saturday morning.   Snowfall
will continue in the west Saturday and spread into central and south areas
east of the Continental Divide with the heaviest snowfall in Natrona and
Fremont counties tapering off in the west Saturday evening and in the
east Sunday morning when colder Canadian air moves in with northerly
winds.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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