Weather Lingo: Lake Effect Snow

Winter snowstorms have a variety of names, such as Nor’easters and Alberta Clippers. It all depends on where and how they develop. In the Great Lakes region of the US, the vast bodies of fresh water influence the weather and create something known as lake effect snow.

Lake-effect snowstorms, according to NOAA, develop when cold air blows across the warmer waters of a large unfrozen lake. The bottom layer of the air mass is warmed by the water and allows it to evaporate moisture, which forms clouds. When the air mass reaches the leeward side of the lake its temperature drops again, because the land is cooler than the water. This releases the water vapor as precipitation and enormous amounts of snow can accumulate. The effect is enhanced if the air is lifted upward by local topography.

With the clouds typically forming in bands, the snowfall is highly localized. Some places can see the snow come down at a rate of more than 5 inches per hour, while nearby, others will only get a dusting. The shape of the lake and the prevailing wind direction help to determine the size and orientation of these bands.

Fetch, the distance wind travels over a body of water, also plays a key role. A fetch of more than 60 miles is needed to produce lake effect snow. In general, the larger the fetch, the greater the amount of precipitation, as more moisture can be picked up by the moving air.

The impressive depths of the Great Lakes allow them to remain unfrozen longer into the winter season than more shallow bodies of water. This combined with their massive surface area, make them excellent producers of  lake effect snow. With northwesterly winds prevailing in the region, communities along the southeastern shores of the lakes are often referred to as being in the “Snowbelt.”

Credit: NOAA

November 2018: Seventh Wettest and Fourth Snowiest on Record in NYC

November was unusually cold in New York City this year. Highs ranged from a relatively balmy 72°F to a chilly 28°F. But, with 22 days posting below average readings, the cold won out in the end. The city’s mean temperature for the month was 44.5°F, which is 3.3°F below average.

In terms of precipitation, November was a month for the record books. The city received 7.62 inches of rain in Central Park, making it the seventh wettest November on recordSnowfall was also abundant, despite the fact that it all fell during a single storm. Central Park reported 6.4 inches of snow, setting set a new daily record for the date. It was also the earliest 6-inch one-day snowfall on record for the city and the largest one-day November snowfall since 1882. Moreover, that one snow event was enough to make this November the city’s fourth snowiest on record.

New York City, on average, sees 4.02 inches or rain and 0.3 inches of snow for the entire month of November.