On Wednesday, June 21, a warm front was located across western Ohio focusing showers and thunderstorms with heavy rainfall across northwest Ohio. That complex of storms pushed east with the front Wednesday evening. That placed northern Ohio in the warm sector, allowing warm and very moist air to be pumped into the region.
As the cold front associated with this system approached Ohio, it slowed down, allowing additional storms to form and track repeatedly over the same locations. The cold front finally passed south across Ohio Friday morning.
Click here for a loop of the surface frontal progression.
The complex of thunderstorms which developed over northern Ohio on the 21st brought torrential rainfall in excess of 6 inches in 6 hours across much of northwest and north central Ohio between Lucas County (Toledo Area) and Ashland County (60 miles southwest of Cleveland). Massive urban flooding was reported in Sylvania and Toledo in Lucas County, Port Clinton in Ottawa County, and Norwalk in Huron County. Primary and secondary roads throughout the region were impassable, and many water rescues and evacuations took place. Flooding across this area was by far the worst since 1969, when 10 to 14 inches of rain fell under a similar weather pattern. Norwalk was particularly hard hit, with over 800 homes flooded or evacuated Wednesday night. Water flowing out from the Norwalk Reservoir Spillway was at a level not seen since 1969, when the dam failed.
Radar estimates of rainfall from the 21st (between Noon and 8 am the next morning) were as much as 5 to 7 inches (blue colorfill) with isolated higher amounts. The swath of rainfall went through Lucas, Sandusky, and Huron counties.
Downstream from Norwalk, the Huron River at Milan (Erie County) rose to its third highest crest on record, at 23.95 feet. The next major river to the east, the Vermilion River at Vermilion, while not having a top ten crest, did have its third highest flow on record. As a result from the tremendous amount of water flowing downstream, docks and boats were washed out into Lake Erie from their moorings in downtown Vermilion.
A nearly stationary thunderstorm which developed over Cuyahoga and Summit County on the 22nd dumped 5 to 6 inches of rain in less than 2 hours, and brought the Cuyahoga River at Independence to a new record high of 23.33 feet. The previous record was 22.41 feet, set in 1959. According to the Cleveland Plain Dealer, nearly 3600 homes in Cuyahoga County sustained damage related to the flash flood. The following hydrograph is from the USGS.
Notable 2 day precipitation totals for the area:
Lucas Co - Univ of Toledo 7.25 (fell in 8 hours)
Huron Co - Southern Norwalk 6.66 (fell in 11 hours)
Erie Co - Vermilion 6.50 (fell in 12 hours)
Huron Co - Norwalk WWTP 5.74
Cuyahoga Co - Solon 5.60
Summit Co - Twinsburg 5.34
Huron Co - Fitchville 5.30
Lucas Co - West Toledo 5.15
Erie Co - Finday State Park 5.12
Seneca Co - Tiffin 4.79
Lorain Co - Penfield 4.60
Lorain Co - Canton Twp 4.65