Oasis Effect
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The impact of the Great Lakes on regional weather can make headlines, like this past winter when more than six feet of lake-effect snow buried the Buffalo, New York area. But, another phenomenon kicks in during the late Spring and Summer. That when the Lakes have a gentler, quieter impact, which some meteorologists call the "Great Lakes Oasis Effect."

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

The Oasis Effect produces a cooling on the Great Lakes coastal zones and over their waters, often reducing the oppressiveness of hot, sticky weather for many. Here's why.

The Lakes cool slowly in late Autumn and early Winter, but eventually their top water layer falls to around the freezing mark. As the year moves into Spring and Summer, the Lakes are also slower to warm, remaining relatively cold compared with daytime air temperatures over land.

When the wind blows over the cold lake waters, its air temperature is reduced, providing natural air-conditioning with the onshore flow. In addition, the temperature contrast between land and lake may produce afternoon lake breezes -- cool winds that blow inland from the lake.

If you live along the Great Lake shores, the phrase "cooler near the lake" is commonly found in local weather forecasts. Shoreline temperatures often drop 10-20 degrees cooler than sites farther inland when onshore breezes flow.

The cooler lake waters also inhibit the growth of afternoon cumulus clouds over them and along the windward shore. Summer satellite observations often show the Lakes and shore regions free of clouds while the surrounding land is dotted with popcorn cumulus.

As well, the cold waters may act like brakes on thunderstorms moving out over the lakes by knocking out a prime energy source, strong daytime surface heating.

The Weather Notebook is a production of the Mount Washington Observatory. It is supported by the National Science Foundation and Subaru, the beauty of all-wheel drive.