By August, the fall buildup begins. Gales are most likely from September through April, particularly in the fall. Strong winds often blow out of the W and NW, making E shore harbor entrances dangerous. However, since Green Bay recorded a 95-knot southwesterly one May, it is not unrealistic to expect a wind extreme of 100 knots or more over open waters. Spring winds can still blow strong, with winds of 28 knots or more encountered about 4 to 8 percent of the time.
Strong winds are infrequent in summer and mostly associated with thunderstorms.
Coastal winds are more localized and variable. Along the Michigan shore, spring winds are variable, particularly in the morning, when northerlies, easterlies, and southerlies are among the most common. By afternoon, aided by a lake-breeze effect, there are a preponderance of winds out of the S, particularly with the approach of summer. Summer also brings a slackening of windspeeds. May. The most likely cause of strong winds in spring and summer are thunderstorm gusts.