SPC MD 1450


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Mesoscale Discussion 1450
NWS Storm Prediction Center Norman OK
1132 PM CDT Fri Jul 12 2019

Areas affected...Portions of western/central SD

Concerning...Severe potential...Watch unlikely 

Valid 130432Z - 130600Z

Probability of Watch Issuance...20 percent

SUMMARY...Supercell thunderstorms may continue to pose an isolated
large hail and damaging wind threat for the next hour or two. A
brief tornado also cannot be ruled out.

DISCUSSION...Storms that formed earlier this evening along a weak
surface confluence zone are moving southeastward around 20-30 kt
from southwestern ND into northwestern SD. These storms are residing
on the northeastward extent of an EML, and are riding along an
instability gradient. Easterly low-level winds quickly veer and
strengthen though mid levels, with 40-50+ kt of effective bulk shear
supporting updraft rotation and thunderstorm organization. Multiple
instances of large hail and damaging winds have occurred with these
supercells across west-central into southwestern ND, along with a
measured 90 mph wind gust and a tornado near Mott ND around 0327Z.

Current expectations are that these storms will probably become
slightly elevated and undergo a slow weakening trend into
western/central SD as the boundary layer continues to cool and
convective inhibition gradually increases. Mid-level westerly flow
also gradually weakens with southward extent into SD. Indeed, the
eastern supercell has recently weakened along the ND/SD border. But,
both isolated large hail and severe/damaging winds may continue to
occur over the next hour or two with the western storm. With strong
low-level shear remaining across this area (effective SRH of 250+
m2/s2), a brief tornado also cannot be ruled out in the short term.
Overall storm coverage should remain isolated, and given current
radar trends watch issuance in western/central SD will probably not
be needed.

..Gleason/Hart.. 07/13/2019

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


LAT...LON   45380274 45890261 45900132 45510088 44570070 44280117
            44300179 44660246 45380274 

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