Great Lakes Waterspout Season Is at Hand

Now is the time of year when waterspouts start putting in an appearance on the Great Lakes. I had largely forgotten about spouts until a few days ago when my friend and fellow weather weenie Mike Kovalchick mentioned them in an email. Bing! A light blinked on in my head: That's right! Waterspouts! I've never seen a waterspout. But then, until last year about this time with my buddy Kurt Hulst, I'd never made a point of going out after them. Kurt and I busted that day, but maybe this year I'll get lucky, provided I increase my chances by taking more opportunities to chase spouts. I have zero experience forecasting waterspouts. Thankfully, there's a snappy little graph called the Waterspout Nomogram that simplifies the process. Developed by Wade Szilagyi of the Meteorological Service of Canada, the Waterspout Nomogram provides a quick visual aid for determining when certain critical parameters are in place for four different classifications of waterspout: tornadic, upper low, land breeze, and winter. The tornadic variety is self-explanatory, and any storm chaser with some experience making his or her own forecasts should have a good feel for when that kind of waterspout is likely. Mike favors the 500 mb cold-core, closed low setup, which to my thinking may be a variant of the first in producing low-top supercells. The remaining two, land breeze and winter, seem to involve different dynamics. For all the waterspout categories, one of the constraints is that for spouts to occur, winds at 850 mbs have to be less than 40 knots, something I find particularly interesting in the case of supercell-based waterspouts. In any event, I'm hoping that this year is my year to finally witness a spout or two. Michigan chasers and weather weenies, it's time to pay attention to the marine forecasts. The "second season" can include action right along the lakeshore even when nothing's popping anywhere else. Make sure you bring your shotgun just in case a waterspout gets too close for comfort (written with a wink and a grin).

Waterspout Prediction and the Waterspout Nomogram

After last Saturday's busted waterspout chase, I've become curious about what goes into predicting waterspouts. It's an area I haven't paid much attention to, but after reading a paper on waterspouts sent to me by Mike Kovalchick, I'm interested in learning their forecasting parameters. I had always thought there were just two categories of waterspout: non-mesocyclone and mesocyclone. But the paper presents four categories: tornadic, upper low, land breeze, and winter. All of them fall within a range of variables depicted on a "waterspout nomogram" that correlates convective cloud depth and the difference between water temperature and 850 mb temperature. Tornadic waterspouts cover a broad swath of the nomogram. The remaining three kinds fall within more specific territory: * Land breeze waterspouts require a minimum convective cloud depth of 5,000 feet, stretching all the way up to 32,500 feet, and water/H85 temp differences between 11 and 19 degrees C. * Upper low waterspouts require a minimum convective cloud depth of 6,500 feet, stretching up to 36,500 feet, and water/H85 temp differences between 9 and 19 degrees C. * Winter waterspouts, as one would expect, are a different animal. Convective cloud depths range from 2,250 feet to 9,750 feet, with water/H85 temp differences starting at 24 C and apparently extending beyond that indefinitely. * All of the above presume 850 mb wind speeds of less than 40 knots. This is obviously an extremely simplified summary which I've extrapolated from the waterspout nomogram. The nomogram brings out variables that I haven't addressed here, and it's well worth checking out in the aforementioned paper (see above for link). Developed by Wade Szilagyi of the Meteorological Service of Canada, the nomogram is in use for predicting Great Lakes waterspouts, and evidently is under consideration for use in the Mediterranean Sea as well. It looks to be an easy-to-understand tool, and one I'll surely be using as the Lake Michigan waterspout season ramps up.