One obscure difference between hurricanes and the run-of-the-mill storms is that hurricanes are what meteorologists call "warm-core" - that is, they're relatively mild in the middle. In contrast, regular low-pressure systems are "cold-core," meaning the air above their center is relatively cold.

On rare occasion, a "cold-core" storm can evolve into a "warm-core" one. For this to happen, the storm usually has to sit over the warm ocean for many days. One of the strangest cases I've ever seen of this transformation occurred around this time a few years ago. What was most unusual was that the storm wasn't over the ocean - it was over the Great Lakes.

For a few days in mid-September 1996, an intense storm stalled over Lake Huron. Water temperatures were about 70oF, too low by typical standards for tropical development. But over time, the water warmed the air enough that the storm developed a warm core. An eye actually appeared, as did spiral bands of gusty showers. From a satellite, it certainly looked tropical, and researchers at Penn State dubbed it "Hurricane Huron." It's believed to be the first time that such a storm has been documented over the Great Lakes.

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