The Weather Notebook: Great Lake Levels

Great Lake Levels
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Lately, the water levels in the Great Lakes have been lower than usual‹a lot lower, the lowest levels in 35 years. Officials aren't rosy about the future, either.

Hi, I'm Bryan Yeaton and this is the Weather Notebook.

From 1997 through 2001, the water level in Lakes Michigan and Huron dropped over 40 inches to 13 inches below the long-term average. Lake Superior's was 5 inches below, Lake Erie's 4 inches below, and Lake Ontario's level, 1 inch below normal.

How did this happen? Officials at NOAA give several reasons: lower precipitation, leading to lower runoff, higher evaporation and higher air temperatures from 1997 to 2000. Specifically, extremely high air temperatures greatly reduced tributary runoff and increased lake evaporation, particularly on Lake Superior. Additionally, last winter's below average precipitation dramatically reduced the winter snowpack that the lakes depend upon for normal spring rise in lake levels.

Recreational lake users and commercial outfits have been hurt. The United States Great Lakes Shipping Association reported that for every inch of lost clearance due to low water, an international vessel loses from 90 - 115 metric tons of cargo carrying capacity ranging to $11,000 per day. Additionally, marinas spent millions to dredge boat slips, channels and harbors along the Great Lakes coasts.

And what about this year? Officials at NOAA say that even an average amount of precipitation in the first quarter of this year won't boost the levels back to normal.

Thanks today to contributing writer Keith Heidorn of Victoria, British Columbia. The Weather Notebook is a production of the Mount Washington Observatory and is supported in part by Subaru of America.