SPC MD 1270

MD 1270 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR EXTREME NORTHEAST SOUTH DAKOTA...CENTRAL AND SOUTHERN MINNESOTA AND FAR WESTERN WISCONSIN

Mesoscale Discussion 1270
NWS Storm Prediction Center Norman OK
0357 PM CDT Sun Jul 09 2017

Areas affected...extreme northeast South Dakota...central and
southern Minnesota and far western Wisconsin

Concerning...Severe potential...Watch likely 

Valid 092057Z - 092230Z

Probability of Watch Issuance...95 percent

SUMMARY...Thunderstorms are expected to develop by 22-23Z across
central MN and possibly as far west as northeast south Dakota and
rapidly become severe. Supercells capable of very large hail will be
the initial primary threat, but gradually transitioning to damaging
wind into the evening. A couple of tornadoes are also possible.

DISCUSSION...Broken mid-level clouds associated with lead shortwave
trough are finally beginning to diminish from the west. This process
is promoting greater boundary layer destabilization from eastern
south Dakota into southwest MN. Latest objective analysis shows a
corridor of 2500 J/KG MLCAPE south and west of a weakening outflow
boundary that extends across southern MN to a weak low in northeast
SD. A quasi-stationary front extends from the surface low eastward
through central MN, and a cold front stretches westward from the
surface low along the ND/SD border.

An upstream shortwave trough is moving southeast into northern MN
and will be accompanied by an increase in frontogenetic forcing near
and east of triple point from northeast SD into central MN.
Thunderstorms are expected to initiate in this zone by 22-23Z. A 50
kt mid-level jet accompanying this feature is resulting in 50+ kt
0-6 km shear with discrete supercells likely to be the initial storm
mode. These storms will be capable of producing very large hail,
isolated wind damaging and possibly a couple of tornadoes. Later
this evening, a strengthening westerly low-level jet will promote
evolution to a forward propagating MCS with an increasing threat for
damaging wind.

..Dial/Weiss.. 07/09/2017

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

ATTN...WFO...ARX...MPX...FGF...FSD...ABR...

LAT...LON   44339545 45379747 46079668 46269543 45459291 44769219
            43779259 43789407 44339545 

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