Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 202140
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
240 PM MST Mon Nov 20 2017

.SHORT TERM...This evening through Thursday
Issued at 236 PM MST Mon Nov 20 2017

The system from the Eastern Pacific has begun to impact the Western
Mountain areas.  Snow amounts are still expected to be relatively low
with 6-9 inches in the mountains and 2-3 inches in the valleys.
Snowfall should tapper off significantly by 12Z Tuesday. High winds
are still occurring in the Cody Foothills and in the Wind Corridor
but are on a downward trend. Another shot of energy arrives Tuesday
night in the west and northwest regions.  With warmer temperatures
expected, snow amounts will be lower than the current system due to
a mix of snow and rain.  Accumulations in the mountains will be in
the 3-4 inch range and valleys will see less than an inch.  By late
evening Wednesday the ridge to our southwest amplifies northeast over
WY bringing the precipitation to an end.  The ridging remains in
place through Thursday so Thanksgiving should be warm and dry. 700mb
temps look to be in the 4 to 5 degree range over the Wind River
Basin and western portion of the Bighorn Basin with the least amount
of cloud cover across the forecast area so I bumped temps in these
regions up a few degrees.

.LONG TERM...Thursday night through Monday
Issued at 236 PM MST Mon Nov 20 2017

Later in the week, the high pressure extending from northern Baja to
Montana will start breaking down as a shortwave trough moves from
Washington into Montana.  The quick moving clipper will be into the
Northern Plains by Friday morning, and should produce a few inches
of snow in the northwestern mountains, along with some lower
elevation rain as temperatures hover just above freezing for morning
lows on Friday.  Some areas will see local strong wind due to the N-
S gradient over the state Friday morning.  High pressure builds back
over the area later Friday into Saturday with northwest-west mid
level flow.  The lowest temperatures of the period should be
Saturday morning with the clearing skies after the trough passage.
The ridge axis is forecast to slowly move eastward from Idaho to
eastern Wyoming, Saturday through early Monday.  Sunday looks to be
quite a nice day over the area! Breezy to windy conditions return to
central and southern Wyoming with the ridge axis to the east and a
larger trough of the Washington coast.  Cloudiness likely to
increase over western WY late Sunday into Monday, though
precipitation not really expected across western Wyoming until very
early Tuesday morning.  The Canadian global 12Z cycle is much more
progressive with this system than either the GFS or ECMWF.

&&

.AVIATION...For the 00Z TAFS Monday evening through 00Z Tuesday evening
Issued at 236 PM MST Mon Nov 20 2017

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

A strong jet stream continues to bring Pacific moisture into western
Wyoming Monday night with snow increasing in the mountains and
valleys. KJAC will be most impacted with IFR conditions likely at
times between 00Z/Mon and 10Z/Tue. Have continued MVFR through Tue,
although the snow should decrease after 10Z/Tue. KPNA/KBPI should
also see a period of MVFR in association with the moisture plume.
KPNA will see MVFR late Monday evening. Mountain top obscurations
will be frequent along and west of the Continental Divide.

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

All terminals will be VFR through the period with little more than
lee-enhanced mid-high cloud decks. Gusty winds are on the decrease
across the region but weaker gusts will likely return tomorrow
afternoon. CWSUs ZLC and ZDV SIGMETs will have more information
about forecast turbulence.

&&

.FIRE WEATHER...
Issued AT 236 PM MST Mon Nov 20 2017

Fuels remain at critical levels across over portions of Fremont,
Johnson and Natrona Counties.

Fire weather conditions will remain enhanced tonight as temperatures
warm slightly, RH values are into the 20s (percent) east of the
Divide and across southern Wyoming, and winds gust out of the west
to southwest 35 to 45 mph at times across the critical fuel zones
(see above). Tuesday will generally be cooler and much more moist
compared to values of today with lighter winds for all locations.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 5 PM MST this afternoon for WYZ002-003-
019-020.

&&

$$

SHORT TERM...Hulme
LONG TERM...McDonald
AVIATION...Hulme
FIRE WEATHER...Hulme



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