Complex sentence: Larger fetches provide the boundary layer with more time to become saturated with water vapor, and for heat energy to move from the water to the air.Lake-effect occurs when air mass reaches the other side of the lake, the air rises and cools again.
Split into simpler sentences: Larger fetches provide the boundary layer with more time to become saturated with water vapor and for heat energy to move from the water to the air. As the air mass reaches the other side of the lake, the air rises and cools again.