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Area forecast discussion 
National Weather Service Riverton Wyoming
210 PM MDT Sat may 30 2015

Short term...tonight through Sunday

A weak shortwave moving through the area this afternoon and
afternoon will touch off a few showers and thunderstorms...mainly
across northern and western portions of the County Warning Area. An
interesting wrinkle as the Storm Prediction Center has issued a
marginal risk area for just north of the border across Montana. At
this still appears that a best upper level support will
pass north of the area. However...we did add the gusty wind and
small hail wording to the grids to cover for any storms that could
get a bit stronger. Coverage should wane this evening with the loss
of daytime heating with the hours after midnight mainly dry. In
areas that do get rain...there could be some patchy fog late but
that is hard to pinpoint at this time so we left it out of the grids
for now.

As for Sunday...things are looking a bit more interesting. The Storm
Prediction Center has included much of the Big Horn basin and areas
north of Casper in a marginal risk area. The things that support
stronger thunderstorms include another shortwave crossing the area
providing some forcing as well as some decent shear and warm
temperatures that will aid in buoyancy. However...there is still the
question of enough instability to bring stronger storms. At this
time...we left severe wording out of the equation and went with
gusty winds and small hail. This will be the warmest day so far this
season for many locations with many of the lower elevations taking a
run at 80 degrees. Also...even in areas that get
thunderstorms...most of the day should be rain free most of the

Long term...Sunday night through Saturday

The high pressure ridge aloft over Wyoming will begin to shift east
as a Pacific low pressure trough moves into the West Coast with
increasing southwest flow aloft. This will bring in warmer and
drier air into the southwest. Most of the convection will occur
over and near the western and northern mountains in the evening.
Some showers will linger over the mountains through the night and
Monday morning. Southwest flow will increase with increased wind
along and near the east slopes of the mountains and through the wind
corridor from Rock Springs to Casper. This will keep the main areas
of convection over the west and north with continued warming.
Some showers and thunderstorms will be over and near the western
and northern mountains Monday evening with some showers lingering
over the northwest through the night into early Tuesday morning.
Southwest flow will continue to dominate on Tuesday with windy areas
again along and near the east slopes of the mountains and through
the wind corridor. Convection again will be limited mainly to areas
over and near the western and northern mountains in the afternoon
and evening hours. Little additional warming will occur. This pattern
continues through Wednesday with the Pacific trough moving across
the Pacific northwest into the northern rockies. Showers and
thunderstorms will become more widespread late Wednesday and
Thursday. A cold front will move south from Montana Wednesday night
and Thursday becoming more of a focus for convection along and north
of the cold front. Temperatures will decrease over the north and east
with increasing precipitation and clouds Thursday and Friday as the
upper trough begins to move into western Wyoming. The trough will
continue to make progress moving east very slowly on Saturday which
should be the coldest day with the best chance for more widespread
showers with embedded thunderstorms. However cooling will decrease
the strength of convection.


Aviation.../xxz issuance/

Expect VFR conditions over the region through 00z Saturday. Isolated
showers and storms will occur over and near the mountains until 02z
Sunday. A few showers will move east off the mountains and across
the lower elevations from 21z today until 03z Sunday. Patchy fog
after 9z tonight in areas that receive a shower but pinpointing that
is difficult at this time. Expect a chance for isolated showers and
thunderstorms after 19z for all taf sites on Sunday.

West of The Divide...kbpi/kjac/kpna/krks routes

VFR conditions will prevail over the region. Isolated showers and
storms will occur after 19z over the western mountains. Some of
these showers or storms will move over the lower elevations after
20z today until 03z Sunday...especially in the vicinity of kjac.
Patchy fog may develop near kjac after 9z tonight. A chance of
thunderstorms will return after 19z Sunday...mainly for kjac
although isolated activity is possible in kbpi and kpna.

Fire weather...

Drier and warmer weather for much of the area into this except a few
thunderstorms could occur in the north and west. Isolated to
scattered showers will return Sunday afternoon across northern and
central portions. This will mark a return to another active weather
pattern through the middle of next week. Smoke dispersal each day
will be good to excellent...except for short periods in the very
early morning hours.

Riw watches/warnings/advisories...


Short term...hattings
long term...c.Baker
fire weather...hattings

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