Late Season Tornadoes in Southeast Wisconsin
November 22, 2010
Something rare happened in southeast Wisconsin on Monday, November 22nd - two tornadoes spun up due to a very dynamic weather set-up which featured warm, moist air (surface temperatures in the mid-60s), strong jet stream winds aloft, all interacting with a strong low pressure and cold front approaching from the west. The first tornado began to affect south-central Walworth County at 334 pm while the second tornado began to affect Kenosha and Racine Counties at 401 pm. The last time a tornado occurred in November in Wisconsin was in 1971. However, no one should have been surprised that there was a tornado on Monday, November 22nd if they were aware of the messages that were issued by the National Weather Service.
Performance Summary - what was issued by the National Weather Service:
1. Early Sunday morning (1 am CST), November 21st, the Storm Prediction Center in Norman, OK, mentioned in their Day-2 Severe Weather Outlook for Monday November 22nd that an isolated tornado or two were possible in the lower Great Lakes Region. This is a lead time of over 38 hours.
2. The Milwaukee/Sullivan NWS Forecast Office (WFO MKX) mentioned the possibility of tornadoes in its Hazardous Weather Outlook that was issued at 433 am Monday morning. This is a lead time of 11 hours.
3. WFO MKX issued a tornado warning for southern Walworth County at 309 pm - for an initial lead time of 25 minutes.
4. WFO MKX issued a tornado warning for northern Kenosha County and all of Racine County at 333 pm - for an initial lead time of 28 minutes.
Statistically, the NWS also calculates the average lead time of a tornado warning for every 1-minute position along the path of a tornado. For the Walworth County tornado, the average lead time was 27.5 minutes. For the Kenosha County-Racine County tornado the average lead time was 35.5 minutes.
There were no reported injuries or fatalities due to the direct affects of the tornadoes or the debris missiles generated by the tornadoes. However, we are aware of an indirectly-related injury in Walworth County when an individual, who attempted to go to their basement for safety, fell down some stairs and was injured. They were hospitalized.
Summary of the two tornadoes:
EF1 Tornado (Enhanced Fujita Scale) - from near Union Grove to near Franksville, or about 27 miles southwest to 20 miles south of downtown Milwaukee. The EF1 scale runs from 86-109 mph.
EF1 Tornado (Enhanced Fujita Scale) - Extreme south-central Walworth County, southeast of the Village of Walworth, or about 53 miles southwest of downtown Milwaukee. This tornado had a path length of about 200 yards in northern Illinois and then moved northeast into Walworth County at a point 0.6 miles east of the intersection of Ridge Rd. and State Line Rd. The EF1 scale runs from 86-109 mph.
click to enlarge
Pictures below are courtesy of Lt. Kevin Williams of the Walworth County Sheriff Department, who is the Emergency Management Director for Walworth County.
Radar imagery for the Walworth County Tornado
The reflectivity image, above left, is from 3:33 pm when the tornado was touching down southeast of Walworth.
The storm had a distinct storm relative velocity couplet, above right, as it moved through southern Walworth county. Red colors are winds moving away from the radar, green/blue colors are toward the radar. Radar location is north of the thunderstorm - shown by the large black dot in the image on the left.
Radar Storm Relative Velocity Image for the "Union Grove" Tornado
As with the Walworth county tornado, there was a very pronounced storm relative velocity couplet on radar, above right, indicating the presence of the tornado. A very strong storm relative velocity couplet appears just over Union Grove with this storm. Notice how the tornado is difficult to discern when looking at the radar reflectivity on the left.
Meteorological setup for this severe weather outbreak:
A strong low pressure system and trailing cold front moved very rapidly northeast from eastern Iowa (late morning) to Green Bay, WI (late afternoon). The image above shows the pressure analysis in black, the dewpoints, or moisture, in blue and green shading, and temperatures in red. Click the image for an animation. Notice how the narrow axis of heat and moisture pushed into southeast Wisconsin ahead of the strong cold front. Additionally, there was a large amount of favorable wind shear in the atmosphere that helped the tornadoes "spin up". Wind shear is a change in wind speed and/or direction with height in the atmosphere.
The images below depict the contrast in temperatures associated with this system. The image on the left shows how high temperatures climbed ahead of the approaching cold front Monday afternoon. Most places in southeast Wisconsin reached the mid 60s, well above normal for that time of year. Meanwhile, the image on the right shows how fast temperatures plummeted behind the front, with lows the next morning in the teens to mid 20s.
November tornadoes in Wisconsin, though rare, are not unheard of. The last one was in 1971 when a tornado occurred near Beloit in Rock county on November 1st. 2 tornadoes also occurred in Wisconsin on Novermber 15, 1960, one in Rock county, the other in Clark county. 4 other November tornadoes occurred in Wisconsin prior to 1920.
Contributtions by: Davis/Zabel/Cronce/Kuhlman/Kapela