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.
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.