I mentioned recently the odd pattern of Canadian thunderstorms. Here in the US, thunderstorms look the way they should -- blob-like, extending in odd directions across state boundaries -- while those in Canada show up in radar as discrete little circles.
Why this should be? The answer is after the jump. First, a note from reader Ryan in Canada, underscoring that in reality storms across the Canadian prairie provinces are far from neat, tame, self-contained little events shown on the weather maps.
I live in Southeastern Saskatchewan, and let me tell you: there's nothing small about those rain patches. They're called supercells for a reason. Now I can't go into the full science of the systems, but in essence hot weather is causing evaporation (and we're rain-soaked right now). Humid air has more volume than dry air, and so as the air takes on moisture it needs to go somewhere and it ends up going up. This forms the big cumulus clouds that are so dangerous. They're dangerous because of all the energy they're dealing with. The molecular jostling gives the cell a charge of electricity. The constant updraft creates hail as rain that's trying to fall is pushed up into the colder atmosphere, freezes, falls back down, and is pushed back up in a vicious cycle (until it's big enough to break the cycle). And, finally, the forces involved also have the potential to create dangerous wind vortexes called mesocyclones. If you're lucky it just results in a violent "plow wind" as we call them. If you're unlucky you get a tornado.
We've been getting them for the last month and they're really something to behold. Our town was pelted with hail that got as big as 2.25 inches in diameter a few weeks ago, and there was also a tornado that touched down south of us. Not good for insurance premiums (especially crop insurance). For the last two days we've had tornado watches, which really doesn't happen very often. Usually we just get severe thunderstorm watches.
So, why do storms on Canadian radar look so different from storms blowing across the center of the US?
Because Canada's weather radars -- like its cities -- are mainly right near its southern border, and are widely spaced across the prairie provinces. It's just like the old drunk-looking-for-keys - under-the-streetlight phenomenon. You can only see storms where there are radars to show them, and the radars are mainly at cities big enough to have airports. Since the cities in Canada's west have the string-of-pearls layout, so do the radar reports. As the NavCanada site shows, after you enter a query for recent radar readings:
The world's biggest hailstorm could be happening near Hudson Bay right now, and it wouldn't show up on the radar maps. You get a similar effect in the U.S. mainly over parts of the Rockies where radar coverage is spotty. Below is a dramatic example of the U.S. also appearing to have small, separate, circular storms, from an aviation weather site that combines local radar readings (many of which show ground clutter -- topic for another time). No larger point here, just interesting.Thanks for many interesting hypotheses that people have sent in.
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