Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 181740

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1140 AM MDT Fri May 18 2018

.DISCUSSION...(Today Through Thursday)
Issued at 346 AM MDT Fri May 18 2018

09Z upper level analysis has large trof across the western CONUS
with ridging across the east. In between, southwest upper flow is
present across the northern and central Plains, with shortwave
trof producing a large area of convection across Nebraska. Skies
are cloudy across the Dakotas with stratiform precip lingering
across south central SD. At the surface, weak low pressure resides
across central SD, with weak boundary snaking from the northern
Rockies, across southern ND into MN. Temperatures at 3am are in
the 50s with generally light winds.

Weak upper ridging crosses the area this morning, but another
upper shortwave approaches the area this afternoon. Surface
boundary will slowly shift south today, but out ahead of it,
modest Cape and 0-6km Bulk shear from the Black Hills east could
support a few strong to severe storms this afternoon. With mostly
cloudy skies expected and relatively worked over atmosphere, it
will take some time for boundary layer to recover. Any stronger
activity that occurs this afternoon will shift south and east as
the cold front settles south. High temperatures will be cooler the 60s and 70s.

Best precip chances shift slowly south and east tonight as cold
front moves through Nebraska and high pressure settles into North
Dakota and eastern Montana. Lows will fall into the 40s.

Stronger upper trof crosses the central Plains on Saturday with
additional precip chances expected for mainly the southern half of
the CWA. Mainly rain/rain showers expected, with some thunder
possible across south central SD. Temperatures will be cooler yet,
with highs in the 50s, and lows Saturday night in the upper 30s
and 40s.

Upper trof finally starts moving out of the region Sunday, and a
warming trend will begin as ridging develops. Meanwhile, another
strong low pressure system will develop over the western states,
which will bring more storm activity to the region towards the
middle of next week.


.AVIATION...(For the 18Z TAFS Through 18Z Saturday)
Issued At 1140 AM MDT Fri May 18 2018

Scattered showers and thunderstorms are expected ahead of a cold
front this afternoon through the early overnight hours, particularly
across southwestern SD and near the Black Hills. MVFR cigs and
brief reductions in vsbys are possible in any showers/storms.

Behind the cold front tonight, gradually deteriorating cigs are
expected, becoming MVFR to IFR area-wide. Some limitations to
vsbys due to BR/FG are also expected. In addition, gusty north to
northeast winds will develop late tonight through tomorrow.




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