Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 141720

Area Forecast Discussion
National Weather Service Riverton WY
1020 AM MST Sun Jan 14 2018

.SHORT TERM...Today through Tuesday night
Issued at 150 AM MST Sun Jan 14 2018

The upper level ridge will continue to persist over the west coast
most of the day today. Winds will be gusty during the day in the
Western Mountains and in the Wind Corridor from Rock Springs to the
Green Mountains through tonight. Tonight a modified arctic system
will move in from the north. Snow will first arrive in the northeast
and spread southwest and west. Precip will be widespread overnight
from Park to Natrona Counties. Through the day Monday this system
will bring snow, wind, and colder air to areas east of the divide.
This system is still looking like it is in short supply of moisture
so snow totals will likely be on the low side. H7 temps are
indicated to be in the -12 to -15 range behind this front so temps
will decrease with this system east of the divide and a bit into the
southern areas. Winds will be gusty in the Bighorn Basin and across
Johnson County with a solid north wind behind the front. Monday
night the arctic system will move out to the east, replaced by
induced ridging between systems. This ridging will persist through
the day Tuesday. The northwest areas may begin to see showers from
the next system late Tuesday night.

.LONG TERM...Wednesday through Sunday
Issued at 150 AM MST Sun Jan 14 2018

Global models show a compact upper low moving across the Northern
Rockies Wednesday, but available moisture appears to be limited.
Thus will only have slight to chance PoPs mainly across the west
with little or no PoPs east.

On Thursday, models show a trough approaching the West Coast with
a moist southwest flow developing with snow developing over
northwest Wyoming. Dry conditions are expected over
eastern/southwest sections of the forecast area. This trough pulls
into the West Coast Thursday night with precipitation becoming
more widespread across western Wyoming. The associated cold front
is expected to pull across the forecast area Friday into Friday
night, well ahead of the Pacific trough. Precipitation is
expected to spill to areas east of the Divide with frontal passage
Friday into Friday night, and as some upper jet dynamics come
into play. The precipitation will slowly exit the area Saturday,
as the trough axis shifts east into the Plains. Precipitation
could begin as rain east of the Divide Friday, but should quickly
change to snow in wake of the front. This could bring light to
moderate amounts of snowfall across the region beginning out west
as early as Thursday before spreading across the entire Friday
into Saturday.

Temperatures look to be above average Wednesday through Friday,
becoming seasonal to slightly below average next weekend.


.AVIATION...For the 18Z TAFS through 18Z Monday afternoon
Issued at 858 AM MST Sun Jan 14 2018

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

Areas of fog and MVFR/IFR ceilings are expected to continue
vicinity KJAC through the next couple of hours. Some guidance
suggests it may not lift today, but for now will leave forecast as
is and have improving conditions by 20Z. A strengthening
downslope NNE flow should hinder fog/low cloud formation vicinity
KJAC after 06Z Monday. An Arctic cold front plunging south along
the east slopes of the Divide will push across the Interstate 80
corridor, KRKS, 06z-09z Monday with areas of MVFR ceilings likely
behind the front. Confidence remains low this morning for this to
occur. Skies are expected to clear from NW to SE through the
morning hours Monday across the area.

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

VFR conditions are expected to prevail through 00Z Monday. An
Arctic cold front will then push south and west into the area,
spreading primarily low MVFR ceilings and visibilities in -SN to
a vicinity KCOD-KCPR line between 03Z-06Z Monday and against the
east slopes of the Divide (KRIW-KLND) 07Z-10Z Monday. Mountains
will become increasingly obscured through Sunday evening. These
conditions will persist across the area through 12Z Monday, before
the snow ends and clouds clear from the area by 18Z Monday.


Issued AT 150 AM MST Sun Jan 14 2018

A modified Arctic cold front will bring light snow south across the
north and east into central basins tonight and Monday. The
precipitation and moisture will thin out and dissipate Monday
afternoon and evening with clearing leaving colder temperatures and
stronger inversions over the area especially east of the Continental
Divide. Winds will be breezy in Johnson county and the Northern
Bighorn Basin behind the front tonight.




LONG TERM...Murrell
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