JULY 19, 1983
DERECHO
"The
I-94 Derecho"
Figure 1. Area affected by the July 19, 1983 derecho (outlined in blue). Curved black lines represent the locations of squall line (based on radar reflectivity imagery) at three-hourly intervals. The "black dots" denote personal injuries due to derecho winds; the flag symbols measured wind gusts, with the direction of the wind from the flags toward the lower end of the staffs. The maximum wind gusts (red numbers) are in mph.
Near dawn on the morning of Tuesday, July 19, 1983, a bow echo moved out of northeast Montana and began producing damaging winds in northwest North Dakota (ND). The airport weather stations at Williston and Minot reported wind gusts to 58 and 75 mph, respectively (Fig. 1) . This would be the beginning of a derecho event that would move across the northern Great Plains and Upper Mississippi Valley, and reach the Chicago metropolitan area by late in the evening on July 19th.
Figure 2. Hourly positions of the squall line associated with the "I-94 Derecho." Initially, the convective system appears as a single bow echo, but later it expands into a longer line with a few embedded bows. The line of storms that forms on the north edge of the squall line and perpendicular to it is a feature common to many progressive derecho bow echo systems and is called a "warm advection wing" (Smith 1990). Such features typically produce heavy rain rather than strong winds.
The single bow echo continued to produce occasional damage as it moved across North Dakota during the morning. By early afternoon it began to expand in scale as it entered Minnesota (MN) . The convection evolved into a squall line with two and sometimes three bow echo segments as the system moved across Minnesota and later Wisconsin (WI), with Interstate 94 near its central axis (Fig. 2). Winds over 100 mph were recorded at the Alexandria Airport in west central Minnesota, and planes and hangers were damaged and destroyed. As the storm moved southeast it continued to cause much damage. In the Minneapolis/St. Paul area, about 250,000 customers lost electrical power.
Trees were blown over and buildings damaged as the derecho raced through Wisconsin. In Madison, (red "M" on Fig. 2), Dr. Robert Schlesinger, a research meteorologist at the University of Wisconsin, observed its approach from the southeastern shore of Lake Mendota. He photographed the laminar, layered "shelf cloud" and gust front approaching from the northwest (Figs. 3 and 4). As the strong derecho winds came ashore, several piers were destroyed. On the University of Wisconsin campus (partially visible in Fig. 4), several buildings were damaged and windows were blown out of the second and third stories of the Memorial Library. Tiles from the library roof were blown off and landed several blocks to the southeast. The strong winds produced waves roughly four feet high on Lake Mendota; even well after the strong winds had diminished, unusually large "whitecaps" continued on the agitated lake (Fig. 5).
Thirty-four people were injured in Minnesota and Wisconsin from this storm. Of these injuries, 12 were from mobile homes being blown over, and eight were from falling trees.
Photo by Robert Schlesinger, used with permission
Figure 3. Photograph taken just before sunset on Tuesday, July 19, 1983, looking toward the west-northwest from the southeast shore of Lake Mendota (near the north end of Carroll Street) in Madison, Wisconsin. The laminar, layered shelf cloud associated with the derecho gust front is approaching rapidly from the northwest. Several sailboats may be seen on the lake.
Photo by Robert Schlesinger, used with permission
Figure 4. Photograph taken from the same location as Fig. 3 and a few minutes after Fig. 3, looking toward the west as the derecho gust front and shelf cloud cross Lake Mendota toward the University of Wisconsin campus.
Photo by Robert Schlesinger, used with permission
Figure 5. View of Lake Mendota looking northwest from near the same location as Fig. 3 and approximately 45 minutes after the derecho gust front had passed. Note the large waves with white caps still present well after the strongest winds had passed.
The bow echo system and derecho began moving into northeast Illinois (IL) between 9 and 10 PM CDT. National Weather Service meteorologist Richard Koeneman experienced this derecho and described his experiences in a weather diary. He noted that the evening of July 19, 1983 was "warm and humid," and that the wind was "dead calm." From his home in Lindenhurst, Illinois (red "L" on Fig. 2 near the Wisconsin border north of Chicago), he had a good view of the approaching storm as there was a large lake behind his yard. He noted lightning visible on the horizon to the north and northwest of his home around 9:30 PM. At 9:40 PM, with the wind being calm in his backyard, he could hear the "rushing" noise of strong winds approaching from the northwest. Three minutes later the gust front hit his house and within a minute or two he estimated that the wind was gusting to 70 mph. The house shuddered, and Richard was worried that it might start flying apart. The house lost electrical power and he noted that the temperature dropped from 83 deg. F at 9:30 PM to 68 deg. F by 9:50 PM. He said that it was the first time he had ever been able to hear the noise associated with an approaching gust front. In this case the gust front already had traveled hundreds of miles but was still quite intense as it passed Koeneman's home.
The derecho winds remained intense as they moved into the northwest side of the Chicago metropolitan area. A gust to 69 mph was recorded at O'hare International Airport at 10:10 PM CDT. After this, the bow echo system began to weaken; the wind gusted to only 55 mph as the system passed over Midway Airport on Chicago's south side. The derecho finally dissipated over northwest Indiana (IN) near midnight July 19-20th, after having traveled 1000 miles in 18 hours with an average speed of 56 mph.
References: Johns and Hirt, 1985; Storm Data for July 1983
Back to Noteworthy Derechos list
Back to Types of Derechos question