Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 152329
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
529 PM MDT Wed Aug 15 2018

.DISCUSSION...(This Evening Through Wednesday)
Issued at 135 PM MDT Wed Aug 15 2018

19z surface analysis had weak meso-high over south central SD,
which has pushed an outflow boundary from convection into NE with
the tail end into northwest NE. Upper low evident over the Black
Hills. Isolated storms occurring directly under upper low and
ahead of low where best implied forcing evident across south
central SD into central NE. Tongue of 1-1.5KJ/kg MLCAPE noted
over northern NE curling north into the Black Hills, albeit with
lower instability. 0-6km bulk shear 15-20m/s along the SD/NE
border. Main concern this afternoon/early evening is supercell
potential. Suspect most active weather will be south of the CWA
with latest CAMs trending in this direction, but can`t rule out
one or two supercells near the NE border through early evening.
East-southeast motion takes them out of the CWA as they evolve.
Overnight, upper low exits the CWA with upper ridge quickly
building into the northern plains. Precipitation and clouds will
clear from west to east over western SD, but will hangup over
south central SD. Temperatures will be pleasantly cool.

Thursday through Friday afternoon, upper/thermal ridge build into
the area bringing warmer temperatures, subsiding air, and dry pops.

Friday night into Sunday, progressive upper trough will move from the
northern Rockies into the plains. Moisture return begins in earnest
Friday night ahead system with well-defined synoptic lift Saturday
afternoon/night. Instability will be moderate, although there is
some model disagreement. Instability/shear profiles suggest a few
severe storms may occur during peak heating. Additional
showers/embedded storms expected as the upper trough closes off into
upper low Saturday night into Sunday. Pretty high pops warranted for
this system given model continuity and forecast QPF. Noticeably
cooler temperatures given cloud cover, precipitation and cooling
thermal profiles.

Early next week, west/northwest flow may bring low chances of
precipitation with near/slightly below normal temperatures.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 525 PM MDT Wed Aug 15 2018

Isolated showers and thunderstorms are expected over parts of
southwestern and south central South Dakota this evening. Outside
of any showers or thunderstorms, VFR conditions are expected
through the period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...Helgeson
AVIATION...10


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