SPC MD 1473

MD 1473 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR CENTRAL PORTIONS OF MN INCLUDING THE WESTERN TWIN CITIES METRO

Mesoscale Discussion 1473
NWS Storm Prediction Center Norman OK
0157 AM CDT Tue Sep 18 2018

Areas affected...Central portions of MN including the western Twin
Cities Metro

Concerning...Severe potential...Watch unlikely 

Valid 180657Z - 180930Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated hail up to around 1 inch diameter will be
possible into the early morning across a portion of central
Minnesota, generally within a narrow corridor from Lac Qui Parle
County to the western part of the Twin Cities Metro.

DISCUSSION...Trends in mosaic radar imagery and MRMS MESH indicated
periodic increases in reflectivity intensities and hail sizes,
respectively, since 550Z within the discussion area.  This corridor
of storms is located within the apex of 25-30-kt southwesterly
low-level jet extending from the central Plains to southwest/central
MN, where warm advection is maximized well north of a surface front
draped across IA into NE.  Although any forcing aloft is likely weak
to negligible, this warm advection is expected to support additional
storms through the overnight into early this morning.  The presence
of steep midlevel lapse rates (7.5-8 C/km) extending east across the
upper Mississippi Valley, moderate elevated instability and
effective bulk shear of 30-40 kt suggest an environment favorable
for large hail from storms rooted above the stable boundary layer. 
The low-level jet is expected to veer to westerly by 12Z and weaken,
suggesting a gradual diminishing trend in the strength of the
stronger elevated storms.

..Peters/Edwards.. 09/18/2018

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

ATTN...WFO...MPX...

LAT...LON   45139597 45279528 45249386 45169329 44859321 44719347
            44639452 44729556 44759588 44979608 45139597 

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