John, I was reading the Duluth News Tribune this morning and there was an article that stated, ".....cold winds expected to gust from 40-60 mph combined with warm lake water could create waves that could build to 15-20 feet in some areas."

The way this sentence is worded, it leaves the reader to believe that water temperature may have some affect on wave height. Is this true, perhaps, because of different densities at different temperatures? Or, maybe the article is just worded in a weird way and it is not true at all.

Thanks.

Also to expand on that question (which I was wondering last night) I saw that the local shoar temp by me was 69 deg but it was 34 deg in the center of the lake. I would think that the high winds would be driving that towards us and causing pretty big undertow. Will that affect wave height also??

matti-

It is not so much the actual water temp, but rather the relationship between the air temp and water temp. When the air is colder than the water, the air molecules interact with the water molecules more and you get bigger waves than when the air is warmer than the water. That is one of the big reasons why the lake is so stormy in the autumn because the lake is warm and the air cold- plus we get some honking low pressure centers to roll through in the autumn!

dab102999-

The winds will blow the warmer surface water to the downwind shoreline and bring the colder water from down below (upwelling) out in the middle of the lake as well as along the upwind shoreline.

-John

If I am correct then what you described is what is meant by the lake is "turning over"

Wind and the resultant wave action and upwelling is one way to "turn over" the water in a lake, but so is temperature difference. Water is most dense at around 39 degrees F and if you get a layer of water at the surface to be that temp, it will want to sink because of being more dense. This can cause the lake to "turn Over" in perfectly calm conditions.

-John

Another aspect of fall's cooler air temps vs. early summer's warmer air temps is the idea that the faster winds aloft (say 1500 ft or so) are actually able to make it down to the lake surface. Think instability of cold air above warm water. In the late spring/earl summer, think stability with warm air over cold water. I've heard tell of charter fishing captains heading out to Stannard Rock and seeing the anemometer spinning like crazy and the winds not reaching the surface. Just something to think about.

Thanks John.

http://www.youtube.com/watch?v=VqTiku-90n4

a short video I took of this tuesdays storm
blowing through Grand Marias, Michigan.

We just came back from Grand Marias. Wow.

There are trees down everywhere.

It was enjoyable watching the waves Friday night at the harbor entrance in Duluth. Two big winds in one week?