A warm front moved north across southern and central lower Michigan during the day of June 21st, allowing a much warmer and very humid airmass to advect into the area.  Thunderstorms developed during the mid afternoon hours due to the building heat and instability and lake breeze convergence.  The first of the thunderstorms developed near Holland around 4 p.m. just a couple miles inland of Lake Michigan where the convergence was the strongest.  Numerous additional thunderstorms developed in the zone of lake breeze convergence.  The storms eventually congealed into a line of storms which marched eastward across the area during the early to mid evening hours.
The storms produced winds of up to around 60 mph in some localized locations.  A gust to near 50 mph at the Gerald R Ford Airport in Grand Rapids produced damage to a couple of hangars that injured four people who were in the hangars at the time.  The storms also produced some hail, with the biggest hail stones measuring over two inches in diameter in Muskegon and just east of Bangor.
The most significant issue with the storms however was heavy rainfall.  A storm that produced very heavy rainfall and did not move very fast in eastern Ottawa county from Allendale to near Marne produced 3 to locally 5 inches of rain within a two hour time frame.  This created flooding on parts of the campus of Grand Valley State University, and produced standing water on the roads in Allendale and Tallmadge township in Ottawa county.  Some other areas that received the highest rainfall totals were near the intersection of Isabella, Montcalm and Gratiot counties.  Western Calhoun county also received significant rainfall and portions of the aforementioned areas saw up to 5 inches of rain falling in a 2 to 3 hour time frame.

Flash Flood in CALHOUN, MICHIGAN
From 21-JUN-11 20:30:00 to 21-JUN-11 21:30:00 (EST-5)
Location: SONOMA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

B Drive South between 4 Mile Road and 4 1/2 Mile Road flooded to a depth of 4.5 feet.

Thunderstorm Wind in MUSKEGON, MICHIGAN
From 21-JUN-11 17:28:00 to 21-JUN-11 17:30:00 (EST-5)
Location: TWIN LAKE
Magnitude: 61.00 EG
Reported by: Trained Spotter

A trained spotter reported an estimated severe thunderstorm wind gust to 70 mph at Twin Lake.  Numerous tree branches were blown down and there was also damage to a pontoon boat and garage roof.

Hail in OTTAWA, MICHIGAN
From 21-JUN-11 16:00:00 to 21-JUN-11 16:13:00 (EST-5)
Location: GRAND HAVEN
Magnitude: 1.25 
Reported by: Trained Spotter

One and a quarters inch hail was reported by a trained spotter near Grand Haven.

Flash Flood in ISABELLA, MICHIGAN
From 21-JUN-11 20:00:00 to 21-JUN-11 21:00:00 (EST-5)
Location: ROLLAND CENTER
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Fremont Road (gravel road) was washed out between Littlefield Road and South Johnson.

Thunderstorm Wind in OTTAWA, MICHIGAN
From 21-JUN-11 16:30:00 to 21-JUN-11 16:30:00 (EST-5)
Location: TALLMADGE
Magnitude: 56.00 EG
Reported by: Trained Spotter

A trained spotter reported that a severe thunderstorm produced an estimated wind gust to 65 mph.

Thunderstorm Wind in ISABELLA, MICHIGAN
From 21-JUN-11 19:00:00 to 21-JUN-11 19:00:00 (EST-5)
Location: WINN
Magnitude: 56.00 EG
Reported by: County Official

The Isabella county emergency manager reported that a roof was blown off a pole barn just southwest of Winn.

Thunderstorm Wind in INGHAM, MICHIGAN
From 21-JUN-11 20:20:00 to 21-JUN-11 20:38:00 (EST-5)
Location: MASON
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported that a severe thunderstorm blew down numerous trees and powerlines mainly just east of US-127.

Thunderstorm Wind in CALHOUN, MICHIGAN
From 21-JUN-11 18:25:00 to 21-JUN-11 18:25:00 (EST-5)
Location: LAKEVIEW
Magnitude: 52.00 EG
Reported by: Emergency Manager

Calhoun county emergency management reported estimated a severe thunderstorm wind gust to 60 mph.

Thunderstorm Wind in MONTCALM, MICHIGAN
From 21-JUN-11 18:35:00 to 21-JUN-11 18:35:00 (EST-5)
Location: GREENVILLE
Magnitude: 52.00 EG
Reported by: Trained Spotter

A trained spotter reported an estimated gust to 60 mph near Greenville.

Flash Flood in OTTAWA, MICHIGAN
From 21-JUN-11 18:15:00 to 22-JUN-11 00:15:00 (EST-5)
Location: VRIESLAND
Flood cause: Heavy Rain
Property damage: 1.50M
Crop damage: 0.00K
Reported by: Trained Spotter

Three to five inches fell in just one to three hours across portions of central and eastern Ottawa county.  This caused extensive flooding of the Grand Valley State University Allendale campus, where over a million dollars worth of damage due to flooding was reported.  A coop observer in Allendale measured 4.43 inches of rainfall with this event and a CoCoRaHs observer near Tallmadge measured 3.74 inches of rainfall.

Flood in CALHOUN, MICHIGAN
From 21-JUN-11 22:00:00 to 22-JUN-11 06:00:00 (EST-5)
Location: FT CUSTER
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported that heavy rain caused water to flow over several roads and a foot or two of standing water on several roads and intersections across far western Calhoun county, mainly near to just west and southwest of the city of Battle Creek.

Hail in VAN BUREN, MICHIGAN
From 21-JUN-11 16:58:00 to 21-JUN-11 17:25:00 (EST-5)
Location: HARTFORD
Magnitude: 2.00 
Reported by: Trained Spotter

Radar estimated that large hail fell from just southeast of Hartford to the north northeast across east central Van Buren county to north of Bloomingdale.  A report of two inch diameter hail was received just east of Bangor.

Flash Flood in KENT, MICHIGAN
From 21-JUN-11 19:00:00 to 21-JUN-11 20:00:00 (EST-5)
Location: CHESTERFIELD HGTS
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Six to eight inches of fast moving water flowing over Wilson Avenue and Lake Michigan Drive.

Hail in MUSKEGON, MICHIGAN
From 21-JUN-11 16:45:00 to 21-JUN-11 16:45:00 (EST-5)
Location: MUSKEGON
Magnitude: 2.00 
Reported by: Trained Spotter

A trained spotter in Muskegon reported that hail up to two inches in diameter fell with an isolated severe storm that moved onshore near the Muskegon harbor before quickly diminishing as it tracked further northeast away from Muskegon.

Hail in NEWAYGO, MICHIGAN
From 21-JUN-11 17:52:00 to 21-JUN-11 18:00:00 (EST-5)
Location: WHITE CLOUD ARPT
Magnitude: 1.00 
Reported by: Trained Spotter

A trained spotter reported one inch diameter hail near White Cloud.

Hail in CALHOUN, MICHIGAN
From 21-JUN-11 17:42:00 to 21-JUN-11 17:42:00 (EST-5)
Location: ATHENS
Magnitude: 1.00 
Reported by: Trained Spotter

A trained spotter in Athens reported one inch diameter hail.

Flash Flood in OTTAWA, MICHIGAN
From 21-JUN-11 17:10:00 to 21-JUN-11 18:10:00 (EST-5)
Location: HUDSONVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Seventeen vehicles had to be pulled out of flood waters in the intersection of Church and Main Street in Jenison.

Thunderstorm Wind in KENT, MICHIGAN
From 21-JUN-11 17:30:00 to 21-JUN-11 17:30:00 (EST-5)
Location: (GRR)KENT CO ARPT GR
Magnitude: 50.00 EG
Reported by: County Official

Thunderstorm wind gusts caused two civilian hangars to become damaged and collapse at the Gerald R. Ford International Airport, causing four injuries.  Three of the four were treated on the scene and released but one person who incurred more significant injuries and a head laceration was taken to the hospital.   The damage occurred at the north end of the airport and affected a row of general aviation hangers.  The injuries occurred due to debris from the two hangars that collapsed.

Flood in KENT, MICHIGAN
From 21-JUN-11 17:30:00 to 21-JUN-11 21:30:00 (EST-5)
Location: WESTGATE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several locations in and near downtown Grand Rapids had flooded roads and intersections, with numerous reports of one to two feet of standing water on some roads and at intersections due to heavy rainfall which fell in a short amount of time.  The heaviest rainfall occurred over far west northwestern Kent county in the Walker area, where radar estimates that 3 to 5 inches of rain likely fell.

Flash Flood in KENT, MICHIGAN
From 21-JUN-11 17:15:00 to 21-JUN-11 18:15:00 (EST-5)
Location: GODWIN HGTS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Multiple cars stalled out in water under bridge at the intersection of 28th and Division.

Flood in ALLEGAN, MICHIGAN
From 21-JUN-11 17:00:00 to 21-JUN-11 20:00:00 (EST-5)
Location: HERPS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain caused a couple of roads to be washed out near and north of Wayland in extreme northeast Allegan county.

Hail in OTTAWA, MICHIGAN
From 21-JUN-11 16:06:00 to 21-JUN-11 16:06:00 (EST-5)
Location: NOORDELOOS
Magnitude: 1.00 
Reported by: Broadcast Media

A trained spotter just east of Allendale reported that a severe thunderstorm produced one inch hail.  Broadcast media from Grand Rapids relayed a report of three quarters inch hail north of Zeeland earlier with that storm.