Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 140542

Area Forecast Discussion
National Weather Service Riverton WY
1042 PM MST Wed Dec 13 2017

.SHORT TERM...Tonight through Saturday

The cold front will continue to push through the area tonight
exiting early tomorrow morning.  Still not expecting much in terms
of accumulation with 2-3 inches in the mountains and about an inch
at lower elevation.  The Bighorn Basin and Johnson County will be
the only areas that will see little to no precip.  Thursday morning
post frontal winds will funnel into the Johnson County area with
gust reaching close to 50mph. These winds will likely persist until
Thursday night.  High pressure will continue to build in as a ridge
from the Pacific moves over WY.  This ridge will then flatten
through Friday allowing our next system to push in from the
northwest Friday night. This system will arrive Friday night and
last through most of Saturday. Ahead of the front wind will be quite
gusty through the Absaroka Mountains, gusting for 55-60 mph. Models
are differing just a bit on speed but all are showing this to be a
slower storm than the one today. As such, total accumulations should
be higher. Mountainous regions will see 8-12 inches with the Tetons
possibly seeing isolated areas as high as 16 inches.  The Western
Valleys could see 2-4 inches while the Bighorn Basin, and the Wind
River Basin through Natrona County could see 1-3 inches.

.LONG TERM...Saturday night through Wednesday

A cold front dropping through the state will continue to bring some
snow into Saturday evening. Timing looks fairly consistent
between the GFS and European although snowfall amounts do have
some differences, as would be expected this far out. At this
point, with quick movement of the system heavy snowfall amounts
are not expected although a few inches Saturday evening is
certainly possible. Snow should come to an end later Saturday

Ridging then builds into the area to bring a mainly dry day for
Sunday. Temperatures will be a challenge with fresh snow cover
likely bringing inversions to the basins and valleys that will be
very hard to break given the very week sun since we will be only 4
days away from the winter solstice. Another cold front will move
toward the area for Sunday night into Monday. The difference with
this one is there appears to be little moisture to work with and
most of the jet support will remain to the north over Montana. For
now, we have some slight POPs across the north with mainly dry
conditions across the southern two thirds of the area. There are
some slight timing differences though with the European about 12
hours faster than the GFS. There are also differences with Tuesday
with the new European trending drier and the GFS keeping some light
precipitation across the north. For now, we split the difference
with only some slight POPS across the north. Ridging should then
bring dry weather from Tuesday night into Wednesday. Another system
may move in Wednesday night, but the models really diverge at this
point with the GFS much faster than the European. At this point,
given the GFS has a large bias of rushing precipitation into areas
way too fast in the long term, we kept things dry through Wednesday
evening. As for temperatures, there still looks to be a contrast
with the basins remaining trapped in the inversions and the
normally breezier areas seeing milder temperatures with better
mixing expected.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1040 PM MST Wed Dec 13 2017

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

Skies will continue to gradually clear north to south
overnight with some patchy fog partially obscuring terrain
vicinity KJAC.  Lower MVFR, local IFR ceilings may linger
vicinity KRKS through early Thursday afternoon before a drier west
wind kicks in and pushes these clouds out of the area. VFR
conditions will then prevail across the area through 12z Friday.

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

Areas of IFR/MVFR -SN will continue vicinity and south of a KCPR-
KRIW-KLND line through 09z with this activity diminishing and
gradually pushing off to the south and east. However, lower MVFR-
IFR ceilings will likely linger across these areas through 16-18z
Thursday before dissipating. Some local LIFR fog will also be
possible through the morning near all terminals through the
morning as clearing occurs. Lower ceilings may linger vicinity
KCPR through mid-afternoon, then VFR conditions will prevail all
areas through 12z Friday.



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

Cooler and more moist today as clouds increase with low to moderate
chances for light precipitation (mainly as light snow) by this
afternoon west of the Divide...move to and continuing east of the
Divide tonight into Thursday morning. Winds will be relatively light
by Wyoming standards for most of the area with the gustiest winds to
be found over Natrona and Johnson Counties. Winds become brisk and
gusty out of the north to northwest across Johnson County Thursday
afternoon while better chances for more significant precipitation
will return later Friday night through Saturday.




LONG TERM...Hattings
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