Extreme waves of 20 to 22 feet have been encountered throughout the lake. Dense fog plagues the mariner most often in spring and early summer over the open lake waters. From April into July visibilities drop below 0.5 mile upto 11 percent of the time. May and June are the worst times, and the cold, central waters are the most likely place. These fogs are usually the result of warm air moving across the still cold lake.
Fog is most prevalent and thickest during the morning hours.
Rain, blowing snow and low clouds also reduce visibilities, particularly from late fall through early spring. Over the open water during this peak season thunderstorms are encountered 2 percent of the time. They are most likely between midnight and sunrise. Onshore thunderstorms can be expected on 4 to 7 days per month in the summer months. They are most likely during the afternoon.