Review of Severe Storms with Large Hail and Wind Damage August 10, 2021

Severe Thunderstorms August 10, 2021

Severe thunderstorms tracked across much of Upper Michigan from late morning through early evening on Tuesday, August 10.

Throughout the event there was an elevated stable layer that mostly prevented the strong winds aloft in the storms from reaching the surface. Therefore, the main threat early on was large hail. The storms produced hail up to baseball size near Watersmeet, and up to ping pong ball size near Witch Lake.

However, as the day went on, the storms became surface-based and took advantage of a shallow surface-based mixed layer to produce some localized wind damage in two pockets. One of those pockets was around Witch Lake and the other around Gwinn and Shag Lake. There were thousands of customers without power in these areas because of downed trees and snapped power poles.

A second storm behind the main line pulsed up and produced quarter size hail in Harvey before quickly weakening again. Large hail was also reported in Trenary.

Map of storm reports, courtesy of the Iowa State Environmental Mesonet webpage

Click this link for a complete list of reports of hail, wind damage, and heavy rainfall from this event.

Environment
Radar
Photos
Social Media Messaging

Environment


Strong upper-level trough to the west and moderate to strong mid- and upper-level flow overspreading the area ahead of a cold front	Storms initiated on the cold front stretching from northwest Wisconsin into northern Iowa then moved east	GIF loop of mean sea level pressure and radar reflectivity showing storms developing in northwest Wisconsin and then moving across the U.P.

High dew points, moderate to strong MLCAPE (but also substantial MLCIN), weak to moderate shear, and poor low-level lapse rates	Steep mid-level lapse rates around 8 C/km or more	Vertical profile near MQT showing elevated CAPE with a substantial SBCIN and a high LFC

Radar

Each image shows...

Top left: near-surface radar reflectivity
Top right: reflectivity at around 35,000 to 39,000 feet
Bottom left: near-surface radial velocity (component of wind towards or away from radar)
Bottom right: estimated maximum storm height in thousands of feet


Near Watersmeet at 1:05 pm CDT	Near Witch Lake at 3:54 pm EDT	Near Gwinn at 4:31 pm EDT. Note that the storm top estimate does not work due to the storm's close proximity to the radar.	Near Trenary at 5:15 pm EDT

Photos


2-inch diameter hail in Watersmeet courtesy of Karl Bohnak	Large hail in Watermseet	Large hail in Watersmeet	Large hail in Witch Lake

Ping pong ball size hail near Witch Lake	Snapped power poles near Gwinn	Map of power outages shortly after the storms moved through	0.5-inch diameter hail near Gwinn

Pea size hail near KI Sawyer	Hail in Harvey, courtesy of Phil Britton	Quarter-size hail in Harvey, courtesy of Linda Nellist	Hail in Harvey, courtesy of Linda Nellist