Chords-
There are a couple of reasons and each reason produces a different type of band. When the surface winds converge, they cause the air to rise (like in the case of some thunderstorms) and when this happens during a LES event, you can get a convergence band of snow. This type of LES is very heavy, falling at the rate of several inches an hour. They are most common over lakes Erie and Ontario because those lakes are long in the east-west, but narrow in the north-south, so when you have a wind blowing down the long axis of the lake during a LES event, a land breeze can form on either side of the lake and cause the air to converge over the lake. Convergence bands do occur on all the other Great Lakes too. The southern 1/2 of Lake MI can have them occur quiete frequently because of it's shape.
Other types of banding that can produce streaks of snow is when you have what is called wind-parallel bands that develop. In this case, the wind is out of the same direction all the way up through the atmosphere that the LES is occurring. The air rises in all areas out over the lake, but because of factors like small scale convergence, you get the air to rise faster in some spots over the lake. Right next to this area of enhanced lift, you can have enough subsiding air to subdue the LES formation. Thus you can get banding to occur with the clouds and thus the LES that the banded clouds are producing.
This type of banding is most common on lakes such as Superior and Huron because of their shape.
Hope this made sense.
-John
