yes i always thought that lake superior had big effect on thunderstorms but i rememeber a few summers ago we had severe storms come from minnestoa and they actually got stronger as they went over the lake temps must have been un the 60's or warm for that ti happen and i also remember a few years back a front comin from the south and we had some pretty bad winds and hail but it came directly from the south how warm would the water have to get for them to actually feed off the lake

While Lake Superior does have a big influence on thunderstorms, it does not have an effect on every thunderstorm. In fact the cold waters might help to enhance elevated base thunderstorms that are forming along a warm front or other complex of storms being fed by a low level jet. The cold lake waters could cause a disconnect of the boundary layer winds and help to enhance the low level jet.

As for how warm the waters have to be to enhance thunderstorms, the rule in the tropics is 80 degrees or warmer is needed to support tropical development, so I would say the same would be true for other thunderstorms. It has been my experience forecasting for the Midwest that lake temps of 60-65 or more stop having an inhibiting effect in most cases.

-John