Lake effect snow falls throughout the winter months across northeastern Ohio. Lake effect snow can begin to fall as early as October and can last all the way until April.
In October, the lake is still very warm. Colder air from Canada flowing over the lake can cause significant instability and subsequently cause precipitation to form. However, with the lake still so warm, the precipitation usually falls as rain, or a rain and snow mix. At times, snow will fall inland while along the lake shore, rain will fall due to warmth from the lake.
As we progress through November, the atmosphere becomes colder and the lake also cools a bit. This is when the big lake snows begin. The atmosphere cools much more quickly than the lake, and this can produce extreme instability.
December and January are the heart of lake effect snow season. Synoptic storms draw frequent shots of cold air southeastward across the lakes. The result is frequent bouts of lake effect snow, some of which can be crippling.
By the end of January, during a normal winter, Lake Erie begins to freeze over. While this does tend to reduce the amount of lake effect snow we see in northeastern Ohio, it does not cut if off completely. Remember back to Part 1 of this series. One of the primary ingredients needed for lake effect snow is lift caused by frictional convergence. Winds blowing across the surface of a frozen lake encounter very little resistance. The same slowing and piling of the air occurs along the shore line of a frozen lake as it does a non-frozen lake. Add a bit of synoptic moisture, or moisture flux through the ice on the lake and you can have lake effect snow.
That being said, most of the snow that falls in late January and February does fall from synoptic scale storms.
By March, warm air begins to return and the ice on the lake gradually breaks apart and heavier lake effect snows can resume. The lake snow storms are usually intermixed with bouts or warm weather and rain storms. This makes March a very dynamic and interesting month here in Ohio. These storms can last into April until the warmth of spring finally wins out.
Every winter is different. A mild winter can mean more snow because the lake freezes later than normal or not at all, while a colder winter can mean less snow because the lake freezes sooner. There are so many variables and combinations that it makes forecasting winter weather in northeast Ohio not only challenging, but fun as well.
I will finish out this series tomorrow with a look at lake effect snow headlines and the criteria used to issue them.