What causes lake-effect snow? - WNEM TV 5

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What causes lake-effect snow?

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Over the last few days, the weather focus in Mid-Michigan has been on the bitter cold that moved in with the Christmas holiday and is still lingering late this week. 

But for some, all of a sudden the cold doesn't seem so bad when you see what happened in Erie, Pennsylvania. Lake-effect snow pounded the region from Christmas Day into Tuesday the 26th, shattering records with over 5 feet of snow. 

While we haven't seen that much lake-effect snow, in Mid-Michigan, we know how dangerous it can be. Just the other day, we had dangerous snow squalls moving through the I-69 corridor and parts of west Michigan have seen plenty over the past few days as well. 

So what causes lake-effect snow?

The two most basic ingredients needed for lake-effect snow, probably aren't too unfamiliar for folks living in traditional lake-effect snow belts... cold air and a relatively warmer lake.

When that cold air passes over the warmer lake waters, it creates an unstable environment. Warm, moist air near the lake surface rises, eventually condenses, forming clouds that eventually produce snow. This environment is most common during the late fall and winter months, when air masses start cooling down at a faster pace than the warm waters below, giving us larger temperature differences. 

While cold air and warm water are the two ingredients that we think of most, the wind, along with the size and shape of the lake matter too. 

The wind speed can determine how far the snow bands penetrate inland, with lighter winds keeping the maximum amount of snow near the shoreline and stronger winds pushing it farther inland.

Wind that's also blowing in the same direction over a long period of time, can really allow snow to pile up in the same general area, whereas a wind that keeps shifting will disperse the snow over a greater area. 

As far as the lake goes, the distance over the lake matters. That distance over the open water from one side to the other is called fetch. The longer that fetch, the longer that cold air has to use that warm, moist air in producing lake-effect snow. 

Wind direction is also important with the fetch. For example, a west southwesterly wind over Lake Erie provides a great fetch of around 130 miles, which can lead to lake-effect piling up in places like Buffalo, New York. 

With all of these factors in play, lake-effect is one of the toughest weather phenomenon to forecast. It also has the ability to be very localized, with whiteout conditions in one part of town, with sunshine breaking out in another part. 

And if everything lines up in just the right way, we can have an event like Erie, Pennsylvania just had. 

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