Intense tornado tears through Appleton, Wisconsin
A large, intense tornado tore through the south side of Appleton, Wisconsin, midday Monday, causing significant damage. Forecasters had outlined an enhanced risk of severe and stormy weather for Monday – but there had only been a low-end marginal risk of tornadoes expected.
Radar analysis suggests a tornado quickly formed between 11:55 and 11:59 a.m. local time. At 12:05 p.m., the tornado intensified – probably into an EF2 or EF3 on the Enhanced Fujita Scale for tornado strength, which assigns a 0-through-5 rating to the damage they produce. An enormous debris ball appeared on radar, depicting pieces of homes and structures that had been lofted into the air.
If the National Weather Service confirms EF3 damage, this would be Wisconsin’s fourth such tornado of the year.
The tornado dissipated over Lake Winnebago between 12:20 and 12:25 p.m. after being on the ground for about 30 minutes. Debris was lofted to between 16,000 and 20,000 feet, commensurate with a high-end EF2 to EF3 tornado.
Just before noon, the Weather Service in Green Bay, Wisconsin, issued a tornado warning for the state’s Manitowoc, Winnebago and Outagamie counties. The tornado touched down less than two minutes later. At 12:01 p.m., the Weather Service upgraded it to a “particularly dangerous situation” tornado warning.
The same storm had already produced hail bigger than baseballs at 10:50 a.m. near Belle Plaine, Wisconsin.
What conditions helped this tornado form?
The overall environment was a classic one for summertime supercells dropping out of the northwest. An extremely humid low-level air mass was in place with a dew point of 80.6 degrees – more humid than virtually anywhere in the Amazon rainforest. That meant exceptional instability, or thunderstorm fuel.
Meanwhile, there was sufficient wind shear, or changing wind with height, to help thunderstorms rotate. That’s because the upper-level jet stream was racing down out of the northeast after being shunted north around a heat dome parked over the Rockies.
Moreover, a sharp south-to-north-oriented surface boundary was present just west of Lake Michigan. The southward-moving storm latched onto, and propagated along, this boundary. The boundary contained extra low-level helicity, or twist. The supercell storm efficiently gobbled up and stretched this spin, eventually producing a tornado.