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ACUS11 KWNS 190848
SWOMCD
SPC MCD 190847
MNZ000-SDZ000-191145-

Mesoscale Discussion 1479
NWS Storm Prediction Center Norman OK
0347 AM CDT Wed Sep 19 2018

Areas affected...North-central to eastern SD and adjacent southwest
MN

Concerning...Severe potential...Watch unlikely

Valid 190847Z - 191145Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated large hail should be the primary risk with the
ongoing storm moving to the east-southeast through north-central
South Dakota, and with any additional sustained storms that can
develop and move into northeast and east-central South Dakota to
southwest Minnesota through the early morning.

DISCUSSION...Trends in mosaic radar imagery indicated mainly
discrete storms and one that has evolved into a linear mode across north-central SD (Dewey County into Potter County). These storms
were elevated, given their presence well north of the southern NE to
northern MO synoptic boundary, with easterly surface winds across
SD/MN and temperatures and dew points in the 50s to lower 60s F.
Forcing for ascent appears to be primarily associated with a
transient midlevel impulse tracking east across SD overnight and
into MN after 12Z, while accompanying stronger westerly 500-mb
winds/shear and steep lapse rates are supporting the threat for
large hail.

The track of the Dewey/Potter Counties storm indicated that it began
to accelerate around 0730Z while moving through northern Ziebach
County, and has a current movement at 0840Z toward the
east-southeast at 45 kt. Although this storm and others that
develop will be elevated, the potential may exist for a locally
stronger wind gust to reach the surface. Similar to early yesterday
morning (prior to sunrise), there likely exists dry air in the
sub-cloud layer above the stable boundary layer per modified 00Z UNR
sounding. Downdrafts penetrating this dry air layer could be
enhanced such that higher-momentum air could reach the surface.
Short-term guidance does not provide very much confidence in the
forecast of the ongoing storms, though consensus of HREF members
would suggest overall coverage of sustained and potentially severe
storms should be isolated into this morning as convection spreads
toward eastern SD and adjacent southwest MN.

..Peters/Edwards.. 09/19/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MPX...FSD...ABR...

LAT...LON 45180113 45590016 45589871 45569747 45559590 45039580
44349596 44089629 44069756 44189889 44520031 45180113



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