JULY 4, 1969 DERECHO
"The Ohio Fireworks Derecho"
Figure 1. Area affected by the July 4, 1969 derecho (outlined in blue), with the approximate hourly positions of the leading edge of derecho winds (gust front) indicated by curved purple lines. Arrows indicate direction of storm winds.
During the afternoon of Friday, July 4, 1969, thunderstorms formed over southeast Lower Michigan (MI). As these storms moved southeastward during the early evening, a strong derecho evolved over extreme southeastern Michigan (MI) and Lake Erie (LE). The derecho then roared southeast across northern and eastern Ohio (OH) and western Pennsylvania (PA) during the next few hours. The hourly positions of the gust front (associated with multiple bow echoes) are shown in Fig. 1 above. Winds gusted to 104 mph in Toledo ("T"), and reached 100 mph in the Cleveland ("C") area. In towns and cities near Lake Erie, many people were in parks getting ready to watch the Independence Day fireworks. Also for the occasion, many small boat owners had anchored their craft just off the Lake Erie shore line to watch the fireworks. As the derecho passed, many thousands of trees were blown down, including 5000 in Toledo alone. In the fireworks areas near the south shore of Lake Erie, eight people were killed by falling trees and over 100 boats were overturned, with three persons drowned. A total of 18 people were killed as a result of the derecho winds in Ohio. Some of the worst damage occurred in Lakewood, Ohio, a suburb of Cleveland. As the derecho moved into Pennsylvania it continued to produce much damage, with 5 people injured in Meadville ("M").
Figure 2. Radar imagery (reflectivity) observed by a Decca Company radar located near Akron, Ohio at 8:30 PM EDT July 4, 1969. (From Hamilton 1970)
A radar in Akron, Ohio observed a "bowed" echo about 35 miles northwest of the radar site at 8:30 PM on the evening of July 4th (Fig. 2 above). This bow echo was associated with the deadly derecho winds in Cleveland and was one of the first "bows" to be documented by radar. As the derecho-producing convective system continued to evolve during the overnight, wind profiles in the low to mid troposphere were such that parts of the convective system became stationary. This allowed strong thunderstorms to "train" in a repetitive fashion over parts of southern Michigan and northeast Ohio for several hours during the early morning of July 5th. The resulting flash flooding was responsible for an additional 27 deaths. Total storm damage from high winds and flooding in Ohio alone was estimated at more than $65 million (1969 dollars), making the July 4-5, 1969 derecho-producing convective system one of the region's most deadly and costly ever.
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References: Hamilton 1970; Storm Data for July 1969