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What is Lake Effect Snow?

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Lake Effect Snow Satellite Image

Bands of snow can be seen forming off the Great Lakes.

NOAA
Question: What is Lake Effect Snow?

What is the Difference Between Lake Effect Snow Storms and Regular Winter Storms?

A recent weather reader asked the following question on lake effect snow –

What's the difference between "lake effect" and "regular" snow storms? I live north of Detroit and all the snow is "lake effect" but I'm a couple 100 miles from a lake big enough.

Answer: Lake effect snow is a unique weather phenomenon that can produce tremendous amounts of snow in the winter. As you may see on your local weather channel, a lake effect snow warning might be grounds for pulling out your snow shovel or stocking up on supplies! There are basically two main differences between lake effect snow storms and winter (low pressure) snow storms.

Introduction - Causes of Lake Effect Snow

As cold, arctic air moves down and over the United States from the colder northern regions, large bodies of water are generally warmer than the air moving over them. Our Great Lakes are an excellent example of large bodies of water that stay comparatively warmer than the arctic air that moves over them from the north. The cold air that moves over the lakes picks up moisture which is later dumped in areas to the south and east of the lakes. (More specific details on the causes of this weather system are explained below.)

Difference #1 Between Snow Storms and Lake Effect Storms

The main difference, however, between a lake effect snow and a “standard” snow storm is that lake effect snow storms are not low pressure system storms. As a cold, dry air mass moves over the Great Lakes regions, the air picks up lots of moisture from the Great Lakes. This saturated air later dumps its water content (in the form of snow, of course!) over areas surrounding the lakes. You can also read the article What is a Snow Squall?

Here is a guide to the formation of lake effect snow storms. You may also want to take a look at a satellite image of lake effect snow or reader-submitted photographs of lake effect snow.

  1. Cold air moves over a body of water such as the Great Lakes.
  2. Moisture and warmth as picked up from the warmer bodies of water. (Remember, the Great Lakes don’t freeze!)
  3. That air is now warmer and therefore rises in the atmosphere. This is called convective instability.
  4. The rising air now cools and the moisture in that air parcel begins to condense into ice crystals and clouds form.
  5. When enough moisture condenses out of the air, it falls in the form of snow over the water and the lee side (downwind side) of the lake.
Difference #2 Between Snow Storms and Lake Effect Storms

While a winter storm may last a few hours to a few days on and off, lake effect snow will often produce snow continuously for up to 48 hours in a particular area. Lake effect snows can precipitate as much as 76 inches (193 cm) of light-density snow in 24 hours with fall rates as high as 6 inches (15 cm) per hour. Because winds accompanying arctic air masses generally originate from a southwest to northwest direction, lake effect snow typically falls on the east or southeast sides of the lakes.

Reference

NOAA National Weather Service

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