Major Severe Weather Outbreak
June 21, 2010
Summary, 5 Tornadoes, 1 downburst:
EF2 Tornado (Enhanced Fujita Scale) in the Eagle area of Waukesha County, 30 miles west southwest of downtown Milwaukee. The EF2 scale runs from 111-135 mph, this tornado is rated at 125-130 mph, which is on the high end of the EF2 scale.
EF1 Tornado (Enhanced Fujita Scale) in the Big Bend Muskego area, Waukesha county, 17 miles southwest of downtown Milwaukee.
EF1 Tornado in Cross Plains, Dane County, 13 miles west of the State Capitol, Madison.
EF1 Tornado in Busseyville, southwest Jefferson county, 55 miles west of downtown Milwaukee
EF1 Tornado in central Lafayette county, about 55 miles southwest of the State Capitol, Madison
Downburst with straightline winds of 70 to 90 mph running from Genesee Depot to Big Bend, Waukesha county, about 20 miles southwest of downtown Milwaukee.
National Weather Service Milwaukee/Sullivan staffing during the event: 7 Meteorologists with a combined 124 years of experience.
Normal staffing during an evening shift: 2 Meteorologists.
Here is a link to the latest storm reports and a graphic storm report map:
Thunderstorms developed across much of south central and southeast Wisconsin during the evening of June 21, 2010. There was a convergence of favorable severe weather parameters very late in the afternoon and early in the evening. The most significant feature was a vigorous upper level disturbance, or short wave in meteorology speak, that helped to support deep vertical motions in the atmosphere. This acted on a warm and very moist atmosphere that contained high amounts of wind shear. This resulted in powerful thunderstorms that contained lots of rotation. The rotation makes storms very intense, often leading to damaging straight line winds, large hail, and in this case 5 tornadoes.
Below are animations of these severe weather parameters with the accompanying radar imagery from the evening. Click images to retrieve the animation.
Visible Satellite Image
0-6km Wind Shear
Mixed Layer Cape
Supercell Composite Index
Significant Tornado Index
This animation is a combination of Storm Relative Velocity and Reflectivity at the time of the Eagle tornado, around 911 PM. The storm relative velocity clearly shows the rotation. Red colors indicate movement away from the radar, green is toward the radar. In this case, the radar indicated winds of 88 mph moving away from the radar, right next to winds of 64 mph moving toward the radar. When they are right next to each other, this is serious spin. The reflectivity shows a distinct Debris Ball. These occur when debris from the damage gets ingested into the storm.
The image below shows the strength of the Downburst that moved from the Genesee Depot area, southeast toward Big Bend and Muskego.
This loop of radar reflectivity covers the period from 704 PM through 1011 PM. Click image for the animation.
A mesonet reporting station located near the path of the tornado was able to depict the approach and departure of the tornado in the barometric pressure reading, as seen in the image below. Note the steep drop in pressure right after 9 pm, followed quickly with a sharp increase. The report is courtesy of P. Jensen, who operates this reporting station for the Eagle Springs Lake Management District. The station is situated on the east side of Eagle Springs Lake, approximately 2.5 miles southeast of the town of Eagle, and about 1.5 miles directly south of the tornado path.
Below is a photograph of the tree damage at Old World Wisconsin taken by Mark Was, with John Malan in company. If you look close enough you'll see how the trees were pushed over by the tornado as it moved along with cyclonic, converging winds. We've added red lines that are parallel to the direction that the trees were pushed over. Note that we see a convergence of tree debris toward the center of the tornado as it moved along the thick red arrow line toward the residental section of Eagle. We can't quite tell which directions the trees are pushed over in the top of the image, but the tornado moved through the forested area at the top of the photograph. Obviouisly the tornado quickly intensified when it reached Old World Wisconsin.
Above aerial photos courtesy of Sharon and Rick Martin
|Big Bend/Muskego Area|
|Looking northeast from just north of the intersection of Ames Road and Salty Hollow Road in Lafayette County, about the time the tornado caused its initial damage at 739 pm CDT. Tornado located about 3 miles to the northeast. Above Photos Courtesy of Brenda Whalen|
Below is a lightning photograph taken by Heather Lindert near intersection of Highways 14 and 51 in Janesville in the evening of June 21st. Sort of close, isn't it?