30 years ago this week, something unprecedented happened over the Great Lakes – "Hurricane Huron." Nothing like it has been documented since. It wasn't a hurricane per se, but it did exhibit a symmetric structure, was anchored to decaying/dissipated fronts, and even developed an eye. Nowadays, we'd probably call it "subtropical.” Subtropical cyclones were formally recognized by the National Hurricane Center starting in 1972, but didn’t start getting named until 2002. Lake waters were around 65 degrees. They're usually at their warmest in September. That's not nearly warm enough to, in most scenarios, sustain a fully-tropical system – but it was VERY cold aloft, making the waters seem *relatively* warmer. That's why the storm began to take advantage of those warmer waters, eventually transitioning to a warm core-ish cyclone. (Non-tropical lows have cold air at the middle. Tropical ones are "warm core.") That's because the storm had begun extracting heat energy from Lake Huron. That caused air in the middle of the storm to expand upward, causing the upper atmosphere to bulge a little bit. That's one way we know it was becoming tropical. Much of its strengthening happened between the mornings of September 12-14, 1996 when the system was "vertically stacked." That means an upper-level low was present above the surface circulation. Most non-tropical lows strengthen fastest when an upper-level low is *approaching* the surface disturbance – not when it's already overhead. That's another reason why we believe this system was subtropical. Lastly, the "core" of the storm, complete with an eye, passed over buoy 45008. The air temperature actually warmed as the center passed, then cooled after. That's an indicator of a warm-core system. We haven't seen a cyclone of this nature since. The closest comparison are the "medicanes" that sometimes develop over the Mediterranean. Generally speaking, the Great Lakes are too small and usually too cool for any tropical cyclogenesis. Plus it was believed a storm could never linger over the waters long enough for any sort of tropical development to ensue. But – as we learned 30 years ago – surprises can happen... and a subtropical storm isn't impossible. A great paper by Todd Miner, Peter J. Sousounis, James Wallman and Greg Mann was published in the Bulletin of the American Meteorological Society in 2000. It's worth checking out.

For Omaha/western Iowa, today's a boom-or-bust day. The wind dynamics are concerning, with appreciable wind shear (changing winds with height) favoring robustly-rotating storms. But a strengthening lid of warm air aloft may prevent strong thunderstorms from taking advantage.

Interesting! A tornado warning is in effect for... Lake Erie!? Yep. That's because this thunderstorm may be producing a tornadic waterspout. Environment Canada (Canada's equivalent to NWS) sometimes issues tornado warnings for marine zones. If you see a waterspout, sail perpendicular to its path.