Lake effect rain is a meteorological phenomenon that occurs when cold air moves over a warm body of water, such as the Great Lakes. The temperature difference between the air and the body of water at around 850 millibars (about a mile above the surface) must be more than 10 degrees Celsius for lake effect rain to occur. This temperature difference creates steep lapse rates, or areas of lift, which can lead to strong bands of rain. Lake effect rain can be very localized and drop heavy amounts of rain at times, depending on how much cold air and lift is involved. Lake effect rain bands have the potential to produce thunder, lightning, and even waterspouts if the temperature difference is great enough.

Lake effect rain is similar to lake effect snow, but it falls as rain instead of snow when the temperature in the layer between the clouds and the surface is too warm to sustain snow. The formation of lake effect rain requires a few key elements, including instability, fetch, wind shear, upstream moisture, upwind lakes, synoptic (large)-scale forcing, orography/topography, and snow or ice cover.

In summary, lake effect rain is a weather phenomenon that occurs when cold air moves over a warm body of water, leading to the formation of rain bands. It can be very localized and produce heavy amounts of rain, thunder, lightning, and even waterspouts.