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ACUS11 KWNS 202229
SWOMCD
SPC MCD 202229
WIZ000-IAZ000-MNZ000-210030-

Mesoscale Discussion 1485
NWS Storm Prediction Center Norman OK
0529 PM CDT Thu Sep 20 2018

Areas affected...Southern Minnesota...extreme northeast
Iowa...western into central Wisconsin

Concerning...Tornado Watch 384...

Valid 202229Z - 210030Z

The severe weather threat for Tornado Watch 384 continues.

SUMMARY...Severe threat continues across Tornado Watch 0384, mainly
in association with the developing squall line across southwest
Minnesota. A downstream Tornado Watch issuance is likely within the
next hour or so.

DISCUSSION...Strong storms have recently begun congealing into
multiple linear segments, from Renville County MN to Washington
County NE. Further upscale growth into a squall line is anticipated
based on current radar observations and recent depictions in latest
CAM guidance. With pressure falls continuing across portions of
southern MN into western WI, a warm front (located along the MN/IA
border into southern WI) will continue to lift northward into far
east-central MN/west-central WI over the next few hours.

The ambient environment along the warm front is characterized by
modest low to mid-level lapse rates (around 6.5 C/km) atop 70s
dewpoints, yielding MLCAPE of up to 1000-1500 J/kg. While 50-60 knot
bulk effective shear is present across the entire discussion area,
strong low-level speed and directional shear have been noted along
the warm front, with nearly 600 m2/s2 0-1km SRH as denoted by 22Z
ARX WSR-88D VWP, and 400-500 m2/s2 effective SRH indicated by latest
RAP Analysis. Considering the strong low-level shear, with bulk
effective shear vectors oriented roughly normal to the approaching
squall line, strong low-level rotation will be possible with any
linear segments interacting with the warm front, and a few QLCS
tornadoes will be possible in addition to severe wind gusts.
Elsewhere, damaging gusty winds and some severe hail will be the
primary threats with the stronger storms.

Given the anticipation of the squall line to remain organized and
surface based across southeast portions of MN into WI, east of
Tornado Watch 0384, a new Tornado Watch issuance will be likely by
00Z.

..Squitieri/Grams.. 09/20/2018

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

ATTN...WFO...GRB...MKX...DLH...ARX...MPX...DMX...FSD...

LAT...LON 43569476 43829520 44459530 44719522 44879422 45149311
45359236 45529161 45619069 45499020 45358980 44898906
44368884 43948888 43438917 43129030 43489326 43569476



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