Three Tornadoes Confirmed On The Evening Of August 18th

National Weather Service storm survey crews concluded 3 tornadoes occurred on Tuesday, August 18th. An EF-1 tornado (winds estimated up to 110 mph) was confirmed in Lake Geneva.  Another EF-1 tornado (winds estimated up to 100 mph) was confirmed 2 miles southwest of Big Bend (near County Road L and Maple Avenue). Finally, an EF-0 tornado (winds estimated up to 80 mph) was confirmed in southwest Waukesha (near the intersection of Genesee Rd and Wisconsin 59). 

These statistics are preliminary: The Lake Geneva tornado was about 5 miles long and up to a quarter mile wide. It occurred around 9 pm and lasted about 5 minutes. It started in downtown Lake Geneva and ended in the Lyons area.

The Big Bend tornado occurred around 9:30 pm and was about 1 mile long. It started about 3 miles SW of the city and ended 2 miles SW of the city.

The Waukesha tornado occurred around 9:48 and was less than 1 mile long. Thankfully, we have not heard of any injuries from these storms.

Our radar indicated multiple areas of rotation as shown in the next few images. The 4-panel image below shows Radar Velocity (top left), Reflectivity (top right), Storm-Relative Velocity (bottom left), and Correlation Coefficient (CC) (bottom right) from the Lake Geneva tornado. In the velocity images, green colors show wind moving toward the radar, while red colors show wind moving away from the radar. Rotation is occurring where there is a tight couplet of these outbound and inbound velocities. Another way we can identify tornadoes from the radar is via the tornadic debris signature (TDS). A TDS occurs when debris is thrown into the air, causing the CC to drastically drop. The tornado that impacted Lake Geneva displayed this signature. There is a distinct area of CC minima in the same area where there is a storm-relative velocity couplet (yellow circle).

All 3 tornadoes can be seen in the radar imagery below. There was not a conclusive TDS for the Big Bend or Waukesha tornadoes.

The image below shows the path and intensity of the rotation aloft, which is not necessarily the rotation observed on the ground. It started in the Lake Geneva area and intensified near Mukwonago and Big Bend.

Estimated Damage Paths for the all three Tornadoes:

Estimated Damage Path for the Lake Geneva Area Tornado:

Estimated Damage Path for the Big Bend Tornado:

Estimated Damage Path for the Southern Waukesha Tornado:

Seminary Park, Downtown Lake Geneva	Seminary Park, Downtown Lake Geneva
Near Main Street and Sage Street in Downtown Lake Geneva	State Hwy 120 just East of US Hwy 12,        NE of Lake Geneva
State Hwy 120 just East of US Hwy 12,        NE of Lake Geneva	State Hwy 120 just East of US Hwy 12,        NE of Lake Geneva

National Weather Service
Milwaukee/Sullivan

~SM/SPM/JJW/Hentz/Cronce/Herzog/MBK