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Lake Breeze Weather

© Keith C. Heidorn

In the past, I have written on the impact of the Great Lakes region on autumn and winter storms. The Lakes have equally major impacts on spring and summer weather in its basin.

On late spring and summer days when the temperature soars, a special wind system may form along the coastline of the Great Lakes or other large lakes. It is known as the lake breeze, a similar condition to the sea breeze known along ocean shores.

The lake breeze forms during daylight in the late spring and summer months because Great Lake waters do not warm as quickly as the surrounding land surfaces. Air cooled by contact with the cold lake waters is denser than that surrounding the lake and thus forms a cell of relatively high pressure over the lake. When the sun heats the land, the air above it warms becoming less dense. Thus, solar heating produces a wide region of lower pressure over the land. With high pressure over the lake and low pressure over land, the regional pressure gradient pushes winds inland off the lake. This is the lake breeze flow.

The formation of the lake breeze depends on two main factors: the air temperature contrast between the lake and surrounding land ? which defines the local pressure gradient ? and the strength of the regional wind caused by continental pressure differences, which can counter the lake-land differential. The strongest lake breezes, those above 25 km/h (15 mph), with the furthest inland penetration, 40 kilometres (25 miles), generally occur during late spring hot spells when lake waters are still winter cold while the land is simmer warm.

Since lake water temperature changes very slowly, solar heating of land creates the temperature differential necessary to form the lake breeze around mid-morning. Clear morning skies and light winds are the most favorable weather conditions for lake breeze formation. If the regional wind is too strong, it prevents the formation of the required pressure gradient to drive the lake breeze.

When the sun's heating diminishes in late afternoon, so does the lake breeze as the land begins to cool. However, around large lakeside cities such as Chicago or Toronto, solar heat stored in urban concrete and steel may permit the lake breeze to continue blowing into the evening hours.

The Lake Breeze Front

We have all experienced cold fronts that sweep by with the passage of large-scale storm systems. A cold front can also occur on a more local scale. When the lake breeze forms and brings the colder lake air onto the land, the boundary zone between the two air masses ? lake air and land air ? is known as the lake breeze cold front, or simply the lake breeze front.

The copyright of the article Lake Breeze Weather in Meteorology is owned by Keith C. Heidorn. Permission to republish Lake Breeze Weather in print or online must be granted by the author in writing.