JULY 4-5, 1980 DERECHO
The "More Trees Down" Derecho
Figure 1. Area affected by the July 4-5, 1980 derecho event (outlined in blue). Curved dark purple lines represent the approximate locations of the gust front at three hourly intervals. The "x" symbols circled in purple represent deaths, and the "black dots" denote personal injuries directly attributable to derecho winds. The flag symbols denote measured wind gusts, with the direction of the wind being from the flag end toward the lower end of the staff. Maximum wind gusts (red numbers) in mph. (From Johns and Hirt 1987)
A bowing line of thunderstorms producing a derecho formed just east of Omaha, Nebraska (NE) around 10 p.m. CDT (03 UTC) on Friday evening, July 4th, 1980. The storm front rushed east at a speed of 55 to 60 mph, reaching eastern Indiana (IN) and northwest Ohio (OH) by 8 a.m. EDT (12 UTC) Saturday, July 5th, and the mid Atlantic coast by early evening on the 5th. Measured wind gusts exceeded 80 mph at several points along the storm's track. Six people were killed (shown as "x"s circled in purple in Figure 1), and 67 were injured (shown as dots in Figure 1) by the derecho's winds.
There are two points worth noting about this derecho:
(1) Although the measured wind gusts (Figure 1) do not represent every point affected, they do show how the maximum gust speeds can vary considerably along the path of a derecho. In this case there are three areas where measured gust values exceeded 80 mph: West central Illinois (IL), central Ohio (OH), and northern Virginia (VA). However, there also exist other areas along the derecho track where the maximum wind gusts were much weaker. Values below severe limits (less than 58 mph) near the center of the derecho path were observed in two areas: East central Illinois (IL)/west central Indiana (IN), and eastern Ohio (OH) into southwest Pennsylvania (PA).
(2) Of the 73 casualties associated with this derecho, Storm Data lists specific details as to the cause of injury or death for 63, including the six deaths. The breakdown includes:
Boats overturned...............................................2
injuries and 4 deaths
Vacation campers overturned............................6 injuries
Mobile homes overturned................................20 injuries
Trees fell on people in campgrounds.................5 injuries and 1 death
Trees and limbs fell on people...........................4 injuries
Trees fell on mobile homes................................4 injuries
Trees fell on a vehicle........................................6 injuries
and 1 death
Utility pole fell on a vehicle.................................1 injury
Windows broken and flying glass.......................5 injuries
Home heavily damaged......................................4 injuries
The above list highlights the greatest risks posed by derechos. Campers and boaters, those outside generally, people in vehicles or mobile homes --- and even those in buildings but near windows --- are the most vulnerable. Two of the deaths and 19 of the injuries with the July 4-5, 1980 event were the result of falling trees or tree limbs. Of those killed or injured in campgrounds, all were victims during the night or early morning, when they were likely to have been sleeping. The boating casualties all occurrred during the day, which is, of course, when most recreational boaters are on the water.
A question that might be asked is "Why is the 4-5 July 1980 derecho called the "More Trees Down' Derecho"? This event was one of an unusually large number of derechos that affected the Corn Belt during the summer of 1980. Similar to 1998, another year with many derechos in the Corn Belt, a high pressure ridge dominated the central and southern Plains region during summer, both at the surface and aloft. This pattern yielded extreme heat and drought across the region. The bow echo systems that produced the derechos occurred on the northern and eastern fringe of the high pressure ridge, and they tended to move southeast across the Corn Belt.
Robert Johns, originator of the About Derechos page, was a forecaster with the NWS's National Severe Storms Forecast Center (now the Storm Prediction Center) at the time of the July 4-5 1980 event. He had a phone conversation with his father shortly after the derecho had affected his parent's farm north of Indianapolis. There was a small grove of large trees on the farm. His father mentioned that they had experienced a series of severe windstorms during the past few weeks and that they lost a tree or two with every windstorm that moved through. And with this latest windstorm (July 4-5, 1980), there were now "more trees down" in the grove. Johns' father was worried that there would not be any trees left standing by the end of the summer. Hence, Johns dubbed the July 4-5, 1980 event the "More Trees Down" derecho.
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Additional information:
Johns and Hirt 1987
Storm Data, July 1980
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