Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290432
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1032 PM MDT Sun May 28 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 159 PM MDT Sun May 28 2017

The weak shortwave axis in the northwest flow appears to be
tracking south across Eastern Montana attm with the asct backdoor
cold front currently pushing south from just south of Cody to
between SHR and BYG and will continue to push south, giving our
CWA a glancing affect to mainly our eastern and northern zones
through early this week. Scattered thunderstorms have mainly been
occurring across Johnson County and Northern Natrona County ahead
of the weak sfc frontal boundary with weaker convection to the
south and west, mainly east of the divide. The weak frontal
boundary will continue to work its way south to the divide tonight
with any significant wdly sct additional thunderstorm activity
propagating south toward the divide through this evening. The
biggest threat has been and will continue to be 40 mph wind gusts
and small hail through this evening. By Monday morning, the jet
stream will dip as far southwest as it will with this wx event
with h7 temps dipping to -0.5C over our northeast CWA allowing
any lingering shower activity over the Big Horn Mtns to snow at
elevations as low as 8200 feet or so after midnight tonight with
snow levels remaining around 10k or so elsewhere. This sfc
boundary will keep temperatures from becoming any warmer than they
were today before the warm up resumes Tuesday as the front
retreats to the northeast. The air will be more stable behind the
sfc boundary so expect any convection that forms north of the Owl
Creek mtns to produce just showers Tuesday afternoon with any
thunderstorms that form mainly relegated to areas along and west
of the divide. On Tuesday, most of any t storms that occur will
again be mainly along and west of the divide with areas east of
the divide destabilizing toward evening with maybe some t storm
activity forming in those areas relatively late as the front
retreats. By Wednesday, the warm up will continue with highs in
the 80s many areas east of the divide and 70s west along with
another round of late day thunderstorms with sfc troughiness
moving east into the area along with the upper level ridge axis
approaching from the west.

.LONG TERM...(Wednesday night through Sunday)
Issued at 159 PM MDT Sun May 28 2017

Splitting trough will be moving onto the West Coast to start this
period and then move slowly east across us Thursday night and
Friday while gradually weakening. An increasing threat of showers
and thunderstorms is expected during this period. These systems
are currently out between 40 and 50N, 160-170W. Johnson County
still looks like it may see some moisture returning from the se
late Thursday/Thursday evening as surface low possibly develops
near or south of the area ahead of our split trough. A few
stronger storms may still form in nrn/ern Johnson. Frontal
boundary drops south into the nrn/ern zones behind our split
trough leading to some decent instability in Johnson again on
Friday. Another shortwave in the split flow may impact the north
Friday night or Saturday but confidence low on this evolution
right now. After that, GFS has trended further north with our late
weekend upper low as expected as mean ridge builds over the area.
There remains a srn split and there may be a weak wave moving in
from the west or sw on Sunday leading to a few storms over and
near the mountains, especially in the west.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday)
Issued at 1030 PM MDT Sun May 28 2017

West of the Continental Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions will prevail through Monday night. Isolated showers
will end by 10Z. Then scattered showers and isolated thunderstorms
will develop after 20Z Monday and continue through 03Z Tue. Gusty
wind to 30 knots and small hail are likely with some of the storms.
Showers will become isolated after 03z and end around 06Z
Tuesday.

East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

VFR conditions will prevail through Monday night. Isolated showers
will end by 10Z. Isolated showers and thunderstorms will develop
after 20Z Monday over and near the mountains. This activity will
end by 04Z Tuesday.

&&

.FIRE WEATHER...
Issued AT 159 PM MDT Sun May 28 2017

Fire danger low across the forecast area through the holiday
weekend as all fuels are currently in green-up and much of the
forecast area has received some form of precipitation over the
last few days. Isolated to widely scattered showers or storms
today most likely to occur along and east of the Divide...best
over the higher terrain. Small hail and gusty winds possible into
the evening. More isolated chances for precip Monday and Tuesday,
mainly along and west of the divide and just to the east of the
divide. Additionally, high temperatures and minimum RH values
will remain at or below seasonal and above 20 percent respectively
through Monday. By Tuesday and Wednesday afternoons, the minimum
RH is expected to dip to the upper teens Tuesday afternoon at the
lower elevations east of the divide as well as across Sweetwater
County and the mid to upper teens in those locations Wednesday.
Winds too will remain relatively light through the period (except
for gusty periods near stronger showers/storms). Smoke dispersion
will be good to very good in the afternoons.

&&

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

&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...AR
FIRE WEATHER...Lipson



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