August 7, 2013 Severe Weather Outbreak

Severe Thunderstorms, Tornadoes Hit East-Central Wisconsin

A line of severe thunderstorms raced across Wisconsin during the late night and early morning hours of August 6-7, 2013, producing wind damage and tornadoes in the east-central part of the state. Hundreds of homes, businesses and farm buildings were damaged. Thousands of trees and power lines were downed, leaving tens of thousands of people without power. Two injuries were reported during the storm.

Six tornadoes occurred within the large area of straight-line winds, all within about 45 minutes. Times were estimated based on radar analysis, storm reports, and eyewitness accounts.

Map ID	Start	End	EF-Scale	Comments
1	1 mi W of New London, 12:24 am	Greenville, 12:33 am	EF2	Significant damage at church south of New London. Hundreds of trees impacted homes in Hortonville. Peak wind estimated at 115 to 120 mph. Image at right is of the church on the south side of New London.
2	5 mi SW of New London, 12:22 am	1 mi S of Hortonville, 12:30 am	EF1	Two injuries occurred at Huckleberry Campground, where camping trailers were blown over. About 100 trees were damaged and uprooted. Peak wind estimated at 90 to 95 mph.
3	3 mi E of Greenville, 12:38 am	2 mi NE of Forest Junction, 12:52 am	EF1	Considerable damage on the north side of Appleton near the Northland Mall. Roof damage at mall and nearby businesses. Thousands of trees were damaged, some falling onto homes in a nearby neighborhood. Peak wind estimated at 100 to 110 mph. Image at right is one of many homes that sustained damage from fallen trees in Appleton.
4	Mackville, 12:38 am	3 mi ESE of Greenleaf, 12:53 am	EF1	Numerous trees and farmsteads sustained damage along the path of this tornado. Several homes were damaged by fallen trees and two homes had damage to garages. A boat dealership sustained heavy damage to the roof of the showroom. Peak wind estimated at 95 to 105 mph.
5	4 mi WSW of Freedom, 12:40 am	4 mi E of Maribel, 1:10 am	EF1	Thousands of trees and dozens of farmsteads sustained damage along a 30+ mile long path (damage was sporadic along the path). Peak winds estimated of 95 to 105 mph. Image at right is a farm house, barn and silo that sustained damage near Freedom.
6	1 mi NNE of Pine Grove, 12:59 am	4 SE of Pilsen, 1:10 am	EF1	Several dozen trees were uprooted or damaged along the path of this tornado. In addition, the storm damaged a silo and two barns. Peak winds estimated of 90 to 100 mph.

Below is a map showing the approximate location of the tornadoes. In addition, damaging straight-line winds occurred outside of some of the tornadoes. County emergency management and local officials provided valuable information during the post-storm analysis. (Click for larger view.)

The weather system that produced the severe weather also produced high winds and hail over Minnesota and western Wisconsin earlier in the evening. Here's a map of U.S. storm reports from the evening of August 6 to the early morning of August 7, 2013.

More About the Event

The fast-moving tornadoes that occurred during this event were associated with a type of thunderstorm complex known as a quasi-linear convective system (QLCS). Tornadoes in QLCS's are often fast moving and wrapped in heavy rain, which was the case early in the morning of August 7. The storms and tornadoes were moving at an estimated 60 to 70 mph toward the east!

Unlike most discrete tornadic supercell storms, tornadoes associated with a QLCS are in a sense, more elusive and sinister, in that they typically evolve more quickly, the parent circulation is smaller in scale, are embedded in heavy precipitation and can move eastward at high speeds. In contrast, classic supercell tornadoes evolve from a somewhat larger mid-level circulation (referred to as a mesocyclone) which gradually descends toward the ground. Typically, this evolution can take several minutes or sometimes longer, thus increasing the likelihood of early detection and increased warning lead times. Because QLCS tornadoes spin-up very rapidly and in the lower levels of the storm closer to the ground, attaining adequate warning lead time can be difficult. In many cases, by the time the circulations are identified on radar, they are often already on the ground causing damage.

Below is a Doppler radar image from 12:46 am showing the line of storms and associated areas of rotation (circled). Click image for larger view.

Below is a Doppler radar loop (velocity on the left and reflectivity on the right) showing the line of storms and associated areas of rotation. Click image for larger view.

Below is a regional radar loop showing the line of storms as they cross the state.