Vibilities of less than 0.5 mile occur up to 5 percent of the time. Visiblities of 2 miles or less ocur 5 to 10 percent of he time during most of the navigation season. The shoreline is susceptible to both autumn radiation fogs and early spring advection fogs. Fog is more frequent along the N shore. Simcoe's visibilities drop to less than 0.5 mile on an average of 46 days annually compared to a range of 15 to 23 days as Buffalo, Erie, or Toledo.
Thunderstorms are responsible for some of the strongest winds on the lake.
They are generally a problem from April through September, but can occur at any time. Over the open lake, they occur 1 to 3 percent of the time with a peak during the summer months. They are most likely between sunset and sunrise. Onshore they most often occur during the late afternoon, on 25 to 30 days annually. During June, July and August, they blow on 5 to 10 days per month.