Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 150921
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
221 AM MST Mon Jan 15 2018

.SHORT TERM...Today through Wednesday night
Issued at 220 AM MST Mon Jan 15 2018

The Canadian Front is still east of the divide and will continue its
slide to the southeast this morning, exiting the area by mid day.
Snow accumulations still expected to be less than an inch in most
areas east of the divide. Fog in the valleys likely to continue
with inversions in place and limited mixing. Expect it to remain
dry through Wednesday with a high amplitude ridge in place over
WY. Models do have a shortwave move through the ridge Wednesday
evening which could bring snow to the northwest for a short time,
however my confidence is not high in this happening.

.LONG TERM...Thursday through Monday
Issued at 220 AM MST Mon Jan 15 2018

High wind potential will continue across the Cody Foothills
Thursday morning. Models are showing a large temp gradient
between Yellowstone and the Cody Foothills, strong winds aloft,
and the right exit region of a jet over northwest Wyoming. A
trough will approach the West Coast Thursday with the flow backing
to west southwest. Precipitation should overspread the far
northwest on Thursday, but most of the area will be dry with
unseasonably warm temperatures for mid-January. The main Pacific
trough will push into the West Coast Thursday night with a moist
southwest flow resulting in widespread precipitation developing
over western Wyoming Thursday night. Models are also hinting at
some right entrance region of a jet streak helping enhance
precipitation over the west Thursday night. Enough warm air will
be in place for precipitation to begin as rain in the western
valleys before turning over to snow during the night as the cold
front works into western Wyoming. The cold front is then expected
to push across the rest of the area Friday into Friday evening as
the main energy from trough pushes into the southern Great Basin
and then into the Four Corners area by 12Z Saturday. Precipitation
chances will overspread areas east of the Divide Friday into
Friday night while gradually decreasing over the west. Just like
the western valleys, the eastern lower elevations could see rain
initially, before most areas east of the Divide change to snow by
around 00Z Saturday. A mid-level circulation moving along the
baroclinic zone across southeast Wyoming, as well as some upslope
flow will keep a good chance of snow across central/south-central
areas of the forecast area into Saturday morning. The ECMWF track
is a bit farther south than the GFS keeping significant snowfall
southeast of the forecast area, while the GFS shows the
possibility of decent snowfall over central areas. The trend has
been for a farther south of the main energy with some splitting
which would be limiting factor of anything major. Right now the
best shot of significant snowfall would be across the western
mountains Thursday night into the day Friday. Also windy
conditions are expected Thursday and Friday in the central wind
corridor from South Pass to Casper, but looks to remain below
high wind criteria right now.

Except for the possibility some mountain snow showers mainly over
the west, the area dries out Saturday night and Sunday. The next
wave could begin to impact the area by Sunday night/Monday. The
GFS is less amplified and faster than the ECMWF which brings some
precipitation east of the Divide during the day Monday. For now
the forecast will only have slight valley/low chance PoPs across
the west.

Temperatures will be above average Thursday with temperatures
falling to seasonal to below average temperatures for the weekend
in wake of the cold front on Friday.

&&

.AVIATION...For the 12Z TAFS through 12Z Tuesday
Issued at 220 AM MST Mon Jan 15 2018

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

MVFR ceilings and patchy fog vicinity KJAC is expected to improve
through 13z as downslope NE flow dry lower levels out and erode
inversions.  An Arctic cold front pushing down the east slopes of
the Divide is expected to move into SW Wyoming, vicinity KRKS, by
12z, with a NE wind shift and some MVFR ceilings developing mainly
north and east of KRKS.  Skies will clear with drier air and
increasing NE winds later this morning.  Clear skies are expected to
prevail over the area this afternoon and tonight, with patchy fog
developing vicinity KJAC and KBPI a few hours after sunset.

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

A band of light snow with MVFR, local IFR ceilings and visibilities,
was pushing southwest and weakening across central Wyoming early
this morning.  Areas of MVFR, local IFR conditions in -SN will
persist vicinity and SW of a KCOD-KCPR line through 12z. The back
edge of this band (clearing skies) should be near a KCOD-KCPR line
at 15z, and through KRIW-KLND by 18z. Clear skies and light wind
will then prevail Monday afternoon and Monday night.

&&

.FIRE WEATHER...
Issued AT 220 AM MST Mon Jan 15 2018

The Canadian Front is still east of the divide and will continue its
slide to the southeast this morning, exiting the area by mid day.
Snow accumulations still expected to be less than an inch in most
areas east of the divide, and 1 to 2 inches in the eastern areas.
Expect it to remain dry through Wednesday with a high amplitude
ridge in place over WY. Models do have a shortwave move through the
ridge Wednesday evening which could bring snow to the northwest for
a short time, however my confidence is not high in this happening.

&&

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

&&

$$

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



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