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 dot" symbols represent personal injuries directly related to the derecho winds. The flag symbols represent measured wind gusts with the direction of the wind from the flags towards the other end of the staff. The maximum wind gusts (red numbers) are in mph. (From Johns and Hirt 1987)

A bowing line of thunderstorms producing a derecho developed just east of Omaha, Nebraska (NE) about 10 PM CDT (03 UTC) on Friday evening, July 4th, 1980. The storm front rushed eastward at a speed of 55 to 60 mph reaching eastern Indiana (IN) and northwestern Ohio (OH) by 8 AM EDT (12 UTC) on Saturday morning, 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 on Fig 1) and 67 were injured (shown as dots on Fig. 1) by the derecho winds.

There are two points we would like to make concerning this derecho event:

(1). Although the measured wind values for this case (on Fig. 1) don't represent every point affected, they do show how the maximum gust speeds can vary considerably along the track 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 are other areas along the derecho track where the maximum wind gusts are much weaker. Note that values below severe limits (less than 58 mph) are located near the center of the derecho axis in two areas..... east central Illinois (IL)/west central Indiana (IN) and eastern Ohio (OH) into southwestern Pennsylvania (PA).

(2). Of the 73 casualties associated with this derecho, specific reasons about what happened to the victims were listed in Storm Data for 63 of them, including the 6 deaths. The breakdown includes:

From boats on water sources overturning................2 injuries and 4 deaths
From vacation campers overturning...........................6 injuries
From mobile homes overturning..................................20 injuries
From trees falling on people in campgrounds..........5 injuries and 1 death
From trees and limbs falling on people.......................4 injuries
From trees falling on mobile homes.............................4 injuries
From trees falling on a vehicle.......................................6 injuries and 1 death
From a telephone pole falling on a vehicle.................1 injury
From windows breaking and glass flying...................5 injuries
From a home being badly damaged.............................4 injuries

This list of how the casualties occurred highlights what many of the greatest risks are to people affected by derecho events. People who were camping, boating, or outside generally, and people that were in vehicles or mobile homes or near windows in buildings make up most of the casualties. Two of the deaths and 19 of the injuries were the result of falling trees or tree limbs. Of the people killed or injured in campgrounds, all were victims during the nighttime or early morning hours when they were likely to have been asleep. All of the boaters who were killed or injured were victims during the daytime which is when it is most likely for recreational boaters to be on the water.

A question you might ask is why is this derecho called the "More Trees Down Derecho". This storm event was one of an unusually large number of cases that occurred in the corn belt region during the summer of 1980. Similar to the summer of 1998, when an unusually large number of derechos also affected the corn belt region, a high pressure ridge dominated the central and southern Plains region during the warm season causing extreme heat and drought in that area. The bow echo systems that caused the derecho events were restricted to areas north and east of this high pressure ridge and they tended to move southeastward over the corn belt.

Robert Johns, who was a forecaster at the NWS's National Severe Storms Forecast Center (former name of the Storm Prediction Center) in Kansas City at the time, had a phone conversation with his father after the July 4-5, 1980 derecho event. His parents lived on a farm north of Indianapolis, Indiana and had 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 came by. And with this latest windstorm (July 4-5, 1980) there were "more trees down" in the grove. He was worried that he would not have any trees still standing by the end of the summer. Hence, the July 4-5, 1980 case became the "More Trees Down Derecho".

References......Johns and Hirt, 1987 and Storm Data for July 1980)

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