Western Wisconsin Derecho

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The Western Wisconsin Derecho was a derecho, or severe weather system, that occurred through several counties of Western Wisconsin on July 15, 1980. It caused nearly $160M in damage (1980 dollars) and one person was killed. At the time, it was considered the worst natural disaster in Wisconsin history, and likely still is. To this day, the storm is still referred to as "The July 15th (1980) Storm," "July 15th, 1980," or simply "The Storm."

The system formed in central Minnesota during the early evening of July 15 and intensified that evening in the eastern part of the state. It was a rapidly-moving storm, roaring through the Twin Cities at 60 mph (97 km/h), and picked up speed as it entered Wisconsin.

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[edit] Prelude

The 15 July storm developed during the devastating heat wave of 1980. Eight of the previous nine days in the Twin Cities had highs above 90°F (32°C). The high on 11 July was 100°F (38°C). On 14 July, the day before the storm, the high was 99°F (37°C); the overnight low was a sticky 79°F (26°C). Conditions for severe weather had clearly been developing for days.

[edit] The Storm

At 2:00 p.m. on the afternoon of July 15, a weak area of low pressure was stationed over eastern South Dakota, adjacent to a warm front that extended southeast through southern Minnesota into eastern Iowa. Ahead (north) of the warm front was an area of hot, dry air: the high temperature for the day at Eau Claire was 94°F (34°C) and 95°F (35°C) in the Twin Cities. South of the front was very humid, hot air: Cedar Rapids, Iowa had a high temperature of 98°F (37°C).

As the afternoon progressed, the warm front moved into the dryer air to the north, pulling with it the moist air over the dry air. Regional meteorologists were aware of the potential for thunderstorms because of the low pressure system and the intense heat and moisture, but no one could have predicted the storm that would develop that night.

As the storm raced through St Croix, Pierce, Dunn, Eau Claire, Chippewa, and Clark counties, it caused a band of damage more than 20 miles (30 km) wide. A maximum wind speed of 110 mph (177 km/h) was recorded at the Chippewa Valley Regional Airport, while 100 mph wind was recorded in the city of Eau Claire. At 9:39 p.m., WEAU-TV issued one of several tornado warnings that evening for Eau Claire County, just as the station's electricity was lost

By 10:00 p.m., with the most intense part of the storm winding down, the area of low pressure was directly over western Wisconsin. Behind the low, air had cooled considerably, with the Twin Cities reporting temperatures in the upper 60s. In addition to being tremendously destructive, the storm was considerably long-lived. Remnants of the storm continued through western Michigan; only in the Detroit area did it finally dissipate.

[edit] Tornadoes

Although much of the storm's damage was caused by straight-line winds (see downburst), several tornadoes were reported:

  • St Croix County
    • F2: 8:45 p.m.
  • Dunn County
    • F2: 8:48 p.m. (1 killed, 12 injured)
  • Eau Claire County
    • F3: 8:25 p.m. (10 injured)
    • F1: 8:40 p.m.
    • F2: 8:50 p.m.
    • F1: 11:08 p.m.
  • Chippewa County
    • F2: 8:40 p.m.
    • F1: 8:45 p.m.
    • F0: 8:45 p.m.
    • F0: 9:07 p.m.
  • Clark County
    • F1: 11:07 p.m.

[edit] Aftermath

One area of Eau Clare that was hit hardest was the Mill Run subdivision on the city's north side. Many homes in the neighborhood were destroyed. Across the highway from Mill Run is the headquarters of the home improvement retailer Menards, which also sustained major damage.

Farm Losses

Farm property was hit very hard, with Dunn County receiving the worst damage. It was estimated that more than $27M of damage was done just to farm buildings in that county, and $8M in crops. More than 10,000 farms were initially without power after the storm.

Political Controversy

Four counties affected by the storm were declared federal disaster areas on 24 July by President Carter. Approximately $3.3M of public property in Eau Claire County was damaged in the storm. FEMA would have covered that entire amount in theory. But at some point that year, the rule was changed on what FEMA would cover – which amounted to only 75%. That left better than $800,000 for Wisconsin to pay. Unfortunately, no one notified the states when the rule was changed.

Theories for the change in coverage include the massive influx of Cubans into the country; the Mount St Helens eruption of 18 May; the severe tornadoes in Grand Island, Nebraska in June; and flooding in western Pennsylvania during August. The federal government's budget was badly impacted by these and other disasters. In all, there were 22 major disaster declarations in 1980.

Compounding problems for the state was that the storm occurred in an election year. Frustrated Wisconsin officials, including Governor Lee Dreyfus, were not prepared for the difficulty in dealing with the federal government during such a time.

[edit] Property Damage (1980 Estimates)

  • Total damage was estimated at $159,522,650
    • Eau Claire County: $60,983,650
    • Dunn County: $38,572,000
    • Pierce County: $29,557,000
    • Chippewa County: $10,675,000
    • Public Property: $7,359,500
    • Timber Losses: $14,518,000

[edit] Links & Sources

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