Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 150844
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
244 AM MDT Tue May 15 2018

.SHORT TERM...Tuesday through Thursday night

Things are mainly quiet this morning across the Riverton forecast area.
All in all today looks to be a bit less active with slightly
warmer temperatures aloft and somewhat higher heights we expect
somewhat less coverage of showers and thunderstorms today. In
addition, we still like the idea of the best chance across the
west and then decreasing chances further east. Steering flow
continues to be rather weak so any convection that does form could
end up being slow-moving and would likely stick close to the
mountains and foothills. Temperatures will also begin an upward
trend with more sunshine expected, averaging around 5 to 10
degrees warmer than yesterday.

The warming trend should continue into Wednesday as well, likely the
warmest day of the week. The main culprit for this will be the
increasing southwesterly flow ahead of a shortwave passing across
Montana and northern Wyoming. This also bring breezy conditions
across the favored areas like from Rock Springs through Casper. It
will also increase the chance of thunderstorms across northern
Wyoming where the best instability and forcing will be with chances
gradually decreasing the further south you go. Many of the lower
elevations will likely see high temperatures climbing into the 80s
on this day.

The chance of showers and thunderstorms will likely continue to
increase into Thursday as an upper level low moves in from
California and into the Great Basin, lowering heights and
increasing moisture into the area. Much of the area will likely have
chances of convection on this day as a result. Temperatures will
remain warm, but maybe a couple of degrees cooler given a bit more
cloud cover. On caveat is that the models sometimes rush these lows
in too fast so moisture may be a bit slower in arriving.


.LONG TERM...Friday through Tuesday

Upper level pattern on Friday will feature ridge over western
Canada with a couple of low pressure systems drifting underneath
ridge across the Intermountain West and Great Basin. The system
affecting our weather on Friday is expected to be drifting NE
across Utah. Surface winds out of the northeast will bring cloudy
conditions and areas of rain, higher mountain snow east of the
Divide while showers and isolated thunderstorms develop west of
the Divide where airmass will be more unstable. Temperatures were
trended cooler on Friday than most model guidance east of the
Divide with cool and wet conditions expected. This system should
shear across the central Rockies into the High Plains Friday night
and Saturday Low level E-NE flow will continue to keep cloudy
conditions with chances of showers along and east of the Divide,
with some afternoon/evening thunderstorms across the west. Chances
of showers will then decrease Sunday and Monday with a warming
trend. Another Pacific upper low is expected to move into the SW
U.S. Monday and Tuesday of next week and begin spreading showers
and thunderstorms northward into the area on Tuesday.

&&

.AVIATION...12Z Issuance

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

VFR conditions to prevail through the period. Isolated showers will
end by 12Z. Patchy fog with local IFR conditions are possible in the
western valleys until 15Z. Scattered showers and thunderstorms will
develop after 18Z in the west and occur through 05Z. Local MVFR
conditions will occur with the thunderstorms. Mountains will be
obscured at times. The shower activity will decrease after 06Z Wed.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

VFR conditions to prevail through the period. Isolated showers will
end by 09Z. Isolated showers and thunderstorms will develop after
19Z, mainly over and near the mountains. Local MVFR conditions will
occur with thunderstorms. The activity will decrease after 04Z with
any lingering showers ending around 06Z. Mountains will be obscured
at times.
&&

.FIRE WEATHER...

Fire concerns are expected to remain below critical today. Building
high pressure will result in a smaller coverage of showers and
thunderstorms today. The best chance will be across the western
mountains and in adjacent foothills. Wind will remain light to
moderate outside of any shower or thunderstorm. Relative humidity
will fall into the teens across eastern Sweetwater County, otherwise
it should remain above 20 percent. Mixing and smoke dispersal will
range from fair in the basins and valleys to good to very good in
eastern Sweetwater County. &&

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

$$

SHORT TERM...Hattings
LONG TERM...Meunier
AVIATION...Ross
FIRE WEATHER...Hattings


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