Great Lakes Experiencing Lake Effect Snow
by David Moran, on Jan 11, 2016 4:03:10 PM
Lake Effect Snow is currently affecting eastern portions of the Great Lakes. There are many mechanisms that contribute to the development of Lake Effect Snow, some of which will be explained here.
Lake Effect Snow tends to be observed in the late fall and early winter and can produce some of the heaviest snows of the season across the Great Lakes. In simple terms, Lake Effect Snow develops when cold polar, or arctic air, flows over a warmer body of water. Snowbands that form in this way are usually quite narrow and can be fairly intense with high snowfall rates. The production of Lake Effect Snow begins when cold air passes over a warm lake, creating instability. Once these snowbands are formed, they are enhanced by lifting caused by frictional convergence (convergence caused by air flowing over adjacent surfaces with different roughnesses). The vertical extent of the bands usually only extend a few kilometers in depth. This is an example of the lake effect snow from earlier on Monday, Jan 11.
Lake Effect Snow- Jan 11, 2016
Here is a closer view of one of the more intense bands.
Close-up View of Intense Band of Lake Effect Snow
Additional factors that contribute to the development of Lake Effect Snow include fetch length, wind speed, and wind shear. The fetch is defined as the distance that the cold air travels over the warm water. In general, a fetch of approximately 100 miles is needed to produce significant Lake Effect Snow in the Great Lakes. Wind speed is also important, but the winds cannot be too weak or too strong. If they’re too weak, land breeze circulations dominate; if they’re too strong, the bands likely won’t organize. Wind speeds of 15-20 knots are optimal for the organization of snow bands. Likewise, wind shear is also important. In order to maintain snowbands, wind shear of less than 30 degrees is optimal. For shear between 30-60 degrees, weaker bands can form, but are less organized. For wind shear more than 60 degrees, band formation is disrupted.
Lake Effect Snow events can be characterized by single band events or multiple band events. In single band events, the low level flow is typically parallel to the major axis of a lake. These bands can be 10-30 miles wide and 30-120 miles in length. Snowfall rates in excess of 3 inches per hour can also be observed. When winds are light, thermal convergence dominates and a land breeze sets up. These bands usually have high snow to liquid ratios and can produce significant snow accumulations. In multiple band events, when the wind flow is over a shorter fetch, multiple bands can develop. The individual bands are usually relatively shallow and therefore weaker.
After the initial event, there are several concerns that need to be addressed. If the snow is wet, there is a greater potential for outages. If rapid melting of the snow occurs, flooding can also occur in some situations.
Fact: In November of 2014, a Lake Effect Snow event produced in excess of 60 inches of snow across Western New York.