SPC MD 1588


MD 1588 Image

Mesoscale Discussion 1588
NWS Storm Prediction Center Norman OK
1108 AM CDT Sat Oct 20 2018

Areas affected...southern Lower Michigan

Concerning...Severe potential...Watch unlikely 

Valid 201608Z - 201815Z

Probability of Watch Issuance...5 percent

SUMMARY...Strong damaging gusts (40-50 mph) are possible over the
next several hours as a broken convective line with embedded cells
moves east across southern Lower Michigan.

DISCUSSION...Visible satellite imagery shows a cumulus field
developing over southern Lower Michigan where surface temperatures
are rising into the middle 50s degrees F.  Radar imagery shows a
low-topped convective line with embedded cells showing weak
organizational characteristics located in a south-southwest to
north-northeast line immediately east of Grand Rapids.  As a potent
mid-level shortwave trough continues to pivot southeast over the
central Great Lakes this afternoon, large-scale forcing for ascent
will maximize coincident with peak heating.  

Modifying RAP soundings over southern Lower Michigan for middle 50s
surface temperatures yields a nearly 9 degree C/km 0-3 km lapse rate
because of very cool mid-level temperatures (-25 degrees C at 500
mb).  Although winds in the lowest 3 km are 40 kt or lower per KGRR
VAD data, it seems plausible as the convection slowly organizes,
potential for strong gusts via horizontal momentum transport may
occur.  The main threat with the strongest storms is localized wind
damage due to 40-50 mph gusts.

..Smith/Guyer.. 10/20/2018

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


LAT...LON   42988486 43008346 42568268 41878309 41788398 42048531

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