Wind Damage >> Storm-Wind Damage Scale

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, Storm-Wind Damage Scale 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 Storm-Wind Damage Scale 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, Storm-Wind Damage Scale 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, Storm-Wind Damage Scale 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 Storm-Wind Damage Scale to produce much damage, with 5 people injured in Meadville ("M"). 

Figure 2. Radar imagery (reflectivity) observed by a Decca Company radar located Storm-Wind Damage Scale 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, Storm-Wind Damage Scale 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 Storm-Wind Damage Scale 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), Storm-Wind Damage Scale making the July 4-5, 1969 derecho-producing convective system one of the region's most deadly and costly ever. JULY 4, 1977 DERECHO "The Independence Day Derecho of 1977" 

Figure 1. Area affected by the July 4, 1977 derecho event (outlined in blue). Curved blue lines represent the approximate Storm-Wind Damage Scale locations of the gust front at three hourly intervals. "P" represents the location of Phillips, Wisconsin. The"Independence Day Derecho of 1977" formed over west central Minnesota (MN) on the morning of Monday, July 4th (Fig. 1). 

As the derecho moved east-southeast, Storm-Wind Damage Scale it became very intense over central Minnesota around midday. From that time through the afternoon the system produced winds of 80 to more than 100 mph, with areas of extreme damage from central Minnesota into northern Wisconsin (WI). 

The derecho continued rapidly southeast across parts of Lower Michigan (MI) during the evening, producing winds up to 70 mph and Storm-Wind Damage Scale considerable damage before finally weakening over northern Ohio (OH) around 1:30 AM EDT on Tuesday, July 5th. 

After this storm occurred, Dr. T. Theodore Fujita, a meteorology professor at the University of Chicago, became aware of the extreme wind damage in northern Wisconsin and Storm-Wind Damage Scale decided to conduct a scientific investigation of the event. By observing the damage pattern from the air, he found that there were three areas where extreme damage and forest blowdowns took place. 

One extended from central Minnesota into extreme northwest Wisconsin (shaded area "A" on Fig. 2b), and Storm-Wind Damage Scale the other two extended across a long corridor of northern Wisconsin (shaded areas "B" and "C" on Fig. 2b). Figure 2. (a) Evolution of radar reflectivity showing bow echo system of July 4, 1977. 

Numbers above echoes are time, CST. (b) Areas of most intense downburst damage, including forest blowdowns (shaded areas) that occurred on July 4, 1977, Storm-Wind Damage Scale as determined by an aerial survey by Dr. T. T. Fujita. Orientation of fallen trees indicated by dashed and solid lines in the shaded areas. 

Heavy solid line depicts path of central part of the bow echo system, with tick marks indicating one-half hour time increments in CST. (From Fujita 1978). Fujita also examined the radar echoes associated with the damage path across eastern Minnesota and northern Wisconsin. He noticed that Storm-Wind Damage Scale the echoes evolved into a bowed out signature (Fig. 2a). 

It was from the study of this derecho that Fujita coined the term "bow echo" that is widely used today. Figure 3. Approximate area affected by severe downburst damage in Minnesota and Storm-Wind Damage Scale extreme northwest Wisconsin during the derecho of July 4, 1977 (Area enclosed in green line and corresponding to shaded area "A" in Fig. 2b). 

The counties affected by the first series of intense downbursts associated with the July 4, 1977 derecho, Storm-Wind Damage Scale mostly in Minnesota, are shown on Fig. 3. Estimated wind gust from 80 to 100 mph roared through this area between noon and 2 PM CDT causing hundreds of thousands of dollars worth of damage to personal property. 

Thousands of trees were blown down, extensively damaging cabins and cars. Shortly after the intense winds began, the roof was blown off the Gull Lake Lodge ("G" on Fig. 3) near the Cass/Crow Wing County line. As the derecho winds reached Platte Lake ("P" on Fig. 3), Storm-Wind Damage Scale a woman sustained a broken leg when her mobile home was overturned. 

Some of the worst damage occurred at Milles Lacs Lake ("M" on Fig. 3) where a resort lodge and Storm-Wind Damage Scale several boats were totally destroyed. One launch caught on the lake during by the derecho winds had to ride out eight to ten foot waves for almost an hour. 

Farther downstream, the storm system's winds stripped and flattened large areas of crops in Kanabec and Pine Counties, and Storm-Wind Damage Scale downed trees in the forested areas of Burnett County Wisconsin. 

Figure 4. Area affected by severe downburst damage over northern Wisconsin during the derecho of July 4, 1977 (shaded areas "B" and "C" on Fig. 2b). From the damage severity, Storm-Wind Damage Scale wind gusts were estimated to have been between 73 and 112 miles per hour in the light red shaded areas, and from 113 to 157 mph in the dark red shaded areas. (From Fujita 1978). 

As the derecho continued across northern Wisconsin during the afternoon of Independence Day 1977, a series of intense downburst winds caused major forest blowdowns, Storm-Wind Damage Scale widespread severe damage to property, and many casualties. 

This band of extreme damage, which was 10 to 20 miles wide and over 160 miles long, Storm-Wind Damage Scale extended from eastern Burnett County through Washburn, Sawyer, Price, and Oneida Counties (Fig. 4). Approximately 850,000 acres of trees were either destroyed or badly damaged, and damage estimates including buildings and vehicles totaled about $24 million dollars. 

One person was killed and 35 were injured. As the bow echo system moved into Sawyer County, Storm-Wind Damage Scale a gust of 75 mph was recorded at 1:40 PM CDT at the Hayward Airport near the north edge of the storm complex. 

Continuing across the county, the downburst winds destroyed many barns and cabins and injured eight people. In the southeastern part of the county, Storm-Wind Damage Scale derecho winds wreaked havoc in the Flambeau River State Forest where winds were estimated to have reached 135 mph. In the forest, one person was killed at Conner Lake when a tree fell on her camper van. 

Nearby, the "Big Block," one of the only areas of virgin forest in Wisconsin, was completely destroyed. The derecho then crossed Price County, damaging or Storm-Wind Damage Scale destroying many homes and injuring 20 people. The gust front reached the county seat of Phillips at 2:55 PM CDT, where severe winds lasted 25 minutes. 

The anemometer at the Phillips Airport registered a speed of 100 mph before being blown away. All homes in the Phillips area were damaged, with thirty beyond repair. After leaving Price County, Storm-Wind Damage Scale the bow echo system entered Oneida County and continued to severely damage homes and blow down large areas of forest. 

Seven people were injured across the county. The gust front entered Rhinelander about 3:30 PM CDT, and Storm-Wind Damage Scale a gust to 115 mph was recorded at the Rhinelander Airport. After crossing Oneida county the severe winds continued through northeast Wisconsin to Lake Michigan (LM) . 

However, the strength of the winds and the extent of the damage were not as great as they had been farther west. After crossing Lake Michigan, Storm-Wind Damage Scale the bow echo system entered Lower Michigan near the towns of Manistee and Ludington just before 8 PM EDT (Fig. 1). 

The gust front with winds of 60 to 70 mph moved southeast across the state during the evening, blowing over many trees that damaged homes, utility lines, and vehicles. One woman was injured when a tree fell on her car. In addition to the damaging straight-line winds, Storm-Wind Damage Scale the bow echo system had tornadoes associated with it from central Lower Michigan into the southeast part of the state. 

Two people were injured by these tornadoes, one from an overturned mobile home and Storm-Wind Damage Scale the other from an overturned camper. As the bow echo system entered northern Ohio during the early morning hours of Tuesday, July 5th, some outbuildings and trees were damaged but the thunderstorm system and the derecho ended shortly thereafter. 

In summary, Storm-Wind Damage Scale the Independence Day Derecho of 1977 traveled 800 miles in 14 hours from the Upper Mississippi Valley region to the Lower Great Lakes. One person was killed and 37 were injured. 

Approximately 1,000,000 acres of forest were badly damaged or destroyed, and total damage estimates exceeded $30 million in 1977 dollars. It was this derecho that caught Fujita's interest in bow echoe storms, and Storm-Wind Damage Scale from his research on this case the term "bow echo" was defined. 

Additional information on the July 4, 1977 derecho, including aerial photographs of the damage in northern Wisconsin, may be found here, Storm-Wind Damage Scale on the NWS Green Bay, Wisconsin Forecast Office's web page.

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