Beyond the Forecast: Lake Effect Snow

These snow records from before this weekend's storm are so high over a short period of time because of the way cold air and warm lake water interact

Happy Monday and welcome to another edition of Beyond The Forecast!

I’m sure you noticed the particularly cold air last week. High temperatures were as much as 15 degrees below average. One benefit of that system was the lack of snow or rain that came our way.

The same can’t be said for our friends in the Great Lakes. The same system that brought us cold brought even colder air there and led to immense amounts of snow since last Wednesday.

The Great Lakes themselves are why the same system caused such different weather across the eastern part of the country. Given the right conditions, Lake Effect Snow can form along large lakes and bring intense snow to a large section of the country.

Lake Effect Snow happens when warm lake water compared to cold temperatures on land pairs up with particularly cold air coming from the north. In the late fall and early winter, the Great Lakes still hold onto plenty of heat from earlier in the year. Most of the time it’s hard to evaporate that water into the air and carry it onshore.

Heat from the summer gets stored in the lakes through the fall. That difference in temperature between land and ground sets up an environment for big changes.

When cold air stretches really high into the atmosphere, the water has an easier time evaporating. That moisture starts to mix in with colder air that’s moving over the globe. Once that air reaches land, it encounters more friction and starts lifting higher into the atmosphere. The air cools and condenses the moisture within. Since the temperatures aloft are still so cold, it’s very easy for the condensation to freeze and fall as snowflakes.

Not much snow falls over the lake since the air is more mixed there, but over the cold land the water in the atmosphere can easily freeze

One of the main reasons this storm caused so much snow was the prevailing wind direction. Air needs to have a constant direction from the surface up into the sky for Lake Effect Snow to build.

How much water that wind passes over directly affects how much snow falls. If the wind crosses Lake Erie in the shorter direction, it can pick up plenty of water and cause some snow, but if that wind blows from the southwest, for example from Toledo or Cleveland towards Buffalo, there is a significantly higher amount of water that wind passes over.

Traveling across the long side of the lake means much more water is picked up and will then fall back down
Crossing the lake from the northwest means less total water to work with

The moisture gets carried across the lake until it reaches land dropping off massive amounts of moisture as snow. Lake Effect Snow tends to be heavier on the southern and eastern sides of the lakes since winds in this part of the country generally come from the north and west.

Lake effect snow can only happen in particularly large or deep lakes. Our region is not set up well to get these events

It takes a big lake to get this much snow to form. Lakes here are too small to get the same effect, and even larger lakes in Minnesota and Wisconsin don’t have enough water to rival spots like Buffalo or Chicago.

Be sure to watch our Winter Weather Outlook to see how our season is shaping up for snow. For details on how this week looks in the short term, you can download our weather app and get Meteorologist Chris Michaels’ latest updates online.

You can always get specific forecast details for your zone, whether it’s the Roanoke Valley, the Lynchburg area, the New River Valley or elsewhere around Southwest and Central Virginia, anytime at Know your zone!

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-- Marshall Downing

About the Author:

Marshall Downing presents the weather Saturday and Sunday evenings at 6:00 PM and 11:00 PM, and you can see him during the week at 12:00 PM and 5:30 PM.