Mesoscale Discussion 1339

Issued

Jul 24, 2021, 11:44 AM EDT (15:44 UTC)

Expired

Jul 24, 2021, 2:15 PM EDT

In force

3 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The NCL Michigan radar (KAPX), 59 km from the middle of the area, began a volume at 15:48 UTC, the scan nearest the moment this went out.

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

566 
ACUS11 KWNS 241545
SWOMCD
SPC MCD 241544 
MIZ000-241815-

Mesoscale Discussion 1339
NWS Storm Prediction Center Norman OK
1044 AM CDT Sat Jul 24 2021

Areas affected...Parts of central/northern lower Michigan

Concerning...Severe potential...Watch possible 

Valid 241544Z - 241815Z

Probability of Watch Issuance...40 percent

SUMMARY...Strong thunderstorms may begin developing by 2-4 PM EDT,
particularly near and southwest through south of the Houghton Lake
vicinity, where a supercell or two posing a risk for a tornado is
possible initially, before strong wind gusts become the more
prominent potential hazard.

DISCUSSION...Near the base of large-scale mid-level troughing
primarily shifting east of the Canadian Prairies into the Hudson
Bay/northwestern Ontario vicinity, a southwesterly to westerly
lower/mid tropospheric jet streak is in the process of propagating
across the Upper Midwest and Great Lakes vicinity.  This includes
speeds on the order of 30-50+ kt in the 850-500 mb layer, with a
couple of associated mid-level cyclonic vorticity maxima.  One is
migrating across and east-northeast of the Houghton Lake area, with
another trailing to the west-southwest (now southeast of Oshkosh,
WI).  It appears that forcing for ascent with the trailing
perturbation may begin impacting areas near/southwest through south
of Houghton Lake, and northwest of Saginaw, as early as the 17-19Z
time frame.

Along a diffuse warm frontal zone across the region, a seasonably
moist boundary layer, with surface dew points near 70F, appears
characterized by CAPE on the order of 1000 J/kg.  Mid-levels are
relatively warm, but lapse rates still appear modestly steep, and at
least some gradual boundary-layer warming may contribute to a
further increase in CAPE through mid afternoon.

Given the moderately strong deep-layer shear (including sizable
clockwise-curved low-level hodographs), the increasing instability
and forcing for ascent may become conducive to the development of
organized convective development by mid afternoon.  Isolated
supercells posing at least some risk for a tornado or two may be
possible initially, before activity tends to grow upscale with
potentially damaging wind gusts becoming a more prominent hazard as
activity spreads eastward.

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

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

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

LAT...LON   45108473 44968330 44038299 43178515 44078592 45108473

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.