A rare phenomenon occurred on Lake Superior yesterday. Check out the MODIS satellite picture above – then watch this video. Here’s a video of what these clouds look like on land (from Iowa – yes, that’s a pond behind a dam on the Des Moines River). These waves occur when there is a layer of cold air at ground level (which often happens over the cold water of Lake Superior). Air is a fluid and behaves like water. So, these undular bore clouds look like someone tossed a stone in a lake. Something “disrupts” the cold air layer. It can be thunderstorms (as was the case in Iowa) or a front. This is a type of gravity wave. You may have seen a large boat on a lake. As the boat moves forward, the boat pushes up water, which gravity then pulls back down and makes a wave (waves). Sometimes the wind at the ground changes back and forth as each wave passes. Bores can be singular or there can be many “ripples”, as was the case on Lake Superior yesterday. Scientists have been looking into whether undular bores can affect the strength of tornadoes. Thunderstorms can create undular bores, and undular bores can create thunderstorms. We’re going to go back and take a look at the Thursday night storms, which developed and intensified rapidly over the relatively cool waters of Lake Michigan in the middle of the night. Some of the worst storms we have had in West Michigan have been straignt-line wind events that occurred in the early morning hours (5/31/1998, 7/16/1980 – that storm produced a wind gust of 103 mph at Benton Harbor and 98 mph at the Coast Guard Station at St. Joseph). Here’s one more video of a bore in Iowa. Bores also occur in water, as in this example – note the surfers! This was a predictable bore due to a tide on an estuary. The pic. above shows some fog over Lake Superior with a pattern of light winds – convective, cumulus clouds on land, but not on the cooler water. Check out this undular bore coming off Lake Michigan. They get them coming off the Gulf of Carpentaria in northern Australia.
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