Mesoscale Discussion 1340

Issued

Jul 24, 2021, 2:21 PM EDT (18:21 UTC)

Expired

Jul 24, 2021, 4:15 PM EDT

In force

114 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

60%

The Grand Rapids radar (KGRR), 39 km from the middle of the area, began a volume at 18:25 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.

• Severe Thunderstorm Watch 390Jul 24, 3:15 PM EDT
• Severe Thunderstorm Watch 391Jul 24, 4:30 PM EDT

719 
ACUS11 KWNS 241822
SWOMCD
SPC MCD 241821 
MIZ000-OHZ000-INZ000-242015-

Mesoscale Discussion 1340
NWS Storm Prediction Center Norman OK
0121 PM CDT Sat Jul 24 2021

Areas affected...Much of central and southern lower Michigan into
adjacent portions of northwestern Ohio and northern Indiana

Concerning...Severe potential...Watch possible 

Valid 241821Z - 242015Z

Probability of Watch Issuance...60 percent

SUMMARY...At least scattered thunderstorm development still appears
probable, now mostly likely around 4-6 PM EDT, with the potential to
organize into clusters capable of producing damaging wind gusts. 
Trends continue to be monitored for the possibility of a severe
weather watch.

DISCUSSION...Initial attempts at intensifying thunderstorm
development across/east of the Houghton Lake vicinity appear to be
waning, perhaps due to weakening of the trailing mid-level cyclonic
vorticity center.  However, the boundary layer across much of
central and southern lower Michigan remains moist, modestly unstable
and weakly inhibited, to the south of the effective warm frontal
zone, and ahead of conglomerate convective outflow trailing across
northern Lake Michigan through southern Wisconsin.  

Although the mid-level trough axis is in the process of shifting
across and northeast of the Lake Huron/Georgian Bay vicinity,
moderately strong (40+ kt around 500 mb) west-northwesterly
mid-level flow will maintain strong deep-layer shear across the
region into this evening.  Beneath this regime, it still appears
that continuing daytime heating will support the initiation of at
least scattered thunderstorm activity, perhaps focused on the lake
breeze advancing inland off Lake Michigan.  Aided by the shear, this
activity may tend to grow upscale, with organizing clusters posing a
risk for potentially damaging wind gusts.

..Kerr/Hart.. 07/24/2021

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

ATTN...WFO...DTX...APX...IWX...GRR...LOT...

LAT...LON   41798656 42398606 43928602 44548520 43718306 42148299
            41198652 41448715 41798656

Mesoscale Discussions in Michigan, 2021Mesoscale Discussions in Indiana, 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.