Forecasting Lake Effect Snow
Answer these 9 questions
Part I Lake Effect Basics
The three factors normally needed to form precipitation include (1) sufficient moisture, (2) lifting mechanism, and (3) instability. Lake effect snow forms when a cold air mass (cP, mP, or cA) moves over a relatively warm lake surface. This creates and/or enhances these three factors by:
(1) As cold (and possibly dry) air moves over the warm lake, some water evaporates modifying the air mass. (This can be important for lake effect snow over the Great Lakes, but is less important over the Great Salt Lake.)
(2) When the lake is warmer than the surrounding cold land a temperature difference is created. This temperature difference creates a pressure difference. This pressure difference causes air to move together toward the center of the lake. This is called Thermal Convergence. As the air converges it rises, creating a lifting mechanism.
(3) When a cold air mass moves over the warm lake a steep lapse rate is created. Steep lapse rates indicate an unstable atmosphere.