Very heavy snow can occur in association with optimized lake effect snow, as thundersnow or in an intense snow band created by very strong uplift. A freakishly heavy snow event will have large flakes, will have numerous flakes and conditions will sustain itself for an hour or more. These three factors combined can produce snows of greater than 6 inches in just an hour. A really good snow rate is 2 inches per hour, thus the snow rate in a freakish event is really eye opening. A heavy lake effect snow occurs as frigid air moves over a large fetch of relatively warm water and then this air converges over the land as it continues to lift. Convective style lifting can wring out large amounts of snow. The bigger events can result in snow measured in feet instead of inches. One reason for this is because the conditions responsible for the snow can sustain itself for many hours. Another form of snow that is not lake effect but is convective in nature is thundersnow. This can result in very large snowflakes and numerous snowflakes that accumulate quickly. If the snow rate is able to sustain itself for an hour or more, many inches of snow can pile up within an hour. Due to poor visibility and a piling accumulation, these snows can temporarily cripple an urban area. Heavy snow in association with a mid-latitude cyclone tends to fall in bands. Locations under the bands can get several more inches of snow than surrounding areas. These bands can result from intense dynamic lifting that in turn leads to a type of convective uplift called slantwise convection. When these bands are slow moving or training than many inches of snow can occur at a location in a short amount of time. |