One of the greatest challenges facing the operational meteorologist in the Great Lakes area is providing accurate lake effect and lake enhanced snow forecasts. The single most important parameter governing the generation of "lake effect" or "lake enhanced" snow is lower tropospheric thermal instability determined by the change of air temperature with height. Thermal instability may be forced by various mechanisms. Most commonly over the Great Lakes, it is generated as a result of heat and moisture fluxes from the water into the bottom of the boundary layer. Other factors are important for modulating the strength of lake effect snow convection but are secondary to its generation. These factors include the depth of moist convection (related to inversion height), preconditioning of the atmosphere by upstream moisture sources, orography, shoreline orientation, fetch, wind shear, and various external forcing and control mechanisms.

Various external forcing and control mechanisms include the superimposition of synoptic scale forcing mechanisms at lower and mid-upper tropospheric levels and forcing mechanisms leading to the development of lower tropospheric mesoscale confluent or convergent zones. Confluent or convergent zones may form as a result of flow interactions between a Great Lake and adjoining land mass, producing a region of frictional convergence or thermal convergence thereby leading to the formation of enhanced lake effect or lake enhanced snow regions. These factors will be discussed along with their forecast implications.

Morphologically, lake effect snow convection can be classified into five types: wind parallel bands (long-axis of a lake), wind parallel bands (short axis of a lake), shoreline parallel bands, mid-lake convergence bands, and mesoscale vortices. Characteristics of each type will be discussed, along with the synoptic meteorological conditions upon which each most frequently develop. While classification of such bands is possible, in the true atmosphere, there likely exists a spectrum of lake effect snow bands ranging from near uniform multiple bands to a single lone band. A climatological perspective of snowfall potential for each class of lake effect snow band type will also be presented.

Forecast techniques for forecasting lake effect snow continue to evolve. Today, many techniques first developed during the era when only "standard level’ data was available to forecasters still provide a basis for lake effect snow forecasting. However, the availability of mesoscale numerical weather prediction model data has greatly expanded the available fields forecasters may investigate. This has resulted in a number of additional parameters worthy of interrogation when forecasting lake effect snow which will be discussed.