Mesoscale Discussion 1732

Issued

Sep 12, 2021, 6:52 PM EDT (22:52 UTC)

Expired

Sep 12, 2021, 8:45 PM EDT

In force

113 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 493...494

Counties Clinton County, MI, Genesee County, MI, Gratiot County, MI, Ionia County, MI, Kent County, MI, Lapeer County, MI, Livingston County, MI, Macomb County, MI, Montcalm County, MI, Oakland County, MI, Saginaw County, MI, Saint Clair County, MI, Shiawassee County, MI

The Grand Rapids radar (KGRR), 84 km from the middle of the area, began a volume at 22:51 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

957 
ACUS11 KWNS 122253
SWOMCD
SPC MCD 122252 
MIZ000-130045-

Mesoscale Discussion 1732
NWS Storm Prediction Center Norman OK
0552 PM CDT Sun Sep 12 2021

Areas affected...Parts of southern lower Michigan

Concerning...Severe Thunderstorm Watch 493...494...

Valid 122252Z - 130045Z

The severe weather threat for Severe Thunderstorm Watch 493, 494
continues.

SUMMARY...An evolving cluster of thunderstorms may become better
organized with increasing potential for damaging wind gusts, in
addition to large hail, while progressing along a corridor near or
just north of Grand Rapids and Detroit through 9-10 PM EDT.

DISCUSSION...A pair of mid-level cyclonic vorticity centers have
contributed to ongoing vigorous thunderstorms development while
migrating eastward along a 50-70 kt westerly 500 mb jet.  The
convection appears to be generally rooted within moist air above/to
the north of a quasi-stationary frontal zone, near the northern
periphery of plume of warm and capping elevated mixed-layer air
emanating from the Great Plains.

One cluster developed fairly far removed from the lead cyclonic
vorticity center, now progressing across Lake Huron, and the warm
elevated mixed-layer appears to be suppressing it as it approaches
the international border area north of Detroit.  The upstream
cluster appears just ahead of the trailing cyclonic vorticity
center, migrating inland off of Lake Michigan, to the
northwest/north of Grand Rapids.  

The stronger mid-level forcing for ascent with the trailing
thunderstorm cluster seems likely to maintain it across lower
Michigan, near/north of Grand Rapids, Lansing and Ann Arbor, into
the Flint vicinity and areas near/north of the Greater Detroit area
by 01-02Z.  Thermodynamic profiles characterized by steep mid-level
lapse rates and sizable CAPE will remain conducive to large hail, in
the presence of strong cloud-bearing layer shear.  Although
low-level lapse rates are generally weak, profiles are still
relatively warm and saturated, and latent cooling due to melting
hail in downdrafts may gradually contribute to downward transfer of
the strong momentum in mid-levels, perhaps eventually accompanied by
increasing risk for potentially damaging wind gusts.

..Kerr.. 09/12/2021

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

ATTN...WFO...DTX...GRR...

LAT...LON   43568540 43428412 43128258 42448281 42558393 42758533
            43028594 43228539 43568540

Mesoscale Discussions in Michigan, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.