Thursday clipper & lake-effect snow machine

Our next Alberta Clipper is streaking toward northern Minnesota for Thursday.

The surface low is tracking north this time, along the U.S. - Canadian border. The best chance of a shot of 2" to 4" of fresh snow will be in the northern half of Minnesota Thursday.

It looks like enough warm air may mix into the lower layers in southern Minnesota to mix some freezing drizzle into the equation in the metro. A wintry mix should arrive in the metro Thursday morning, and most of the models are cranking out an inch or so of fresh snow for southern Minnesota.

Temperatures should climb briefly into the lower 30s for a few hours Thursday, so hopefully road crews will have plenty of time to treat and keep roads wet, in good shape.

Lake-effect snow machine in high gear.

Check out this remarkably clear MODIS satellite image. You can see the plumes of lake-effect snow streaming southeast over Lake Superior and Michigan. As much as 3 to 4 feet of snow has blasted areas downwind from the Great Lakes this week.

NASA MODIS image shows lake effect "plumes."

(Click for detailed image)

You can also see frozen, snow covered lakes in much of Minnesota, including Upper & Lower Red, Leech, and Mille Lacs.

Deep snow cover is clearly evident in southern Minnesota, and snow free ground still lingers in eastern Wisconsin.

Lake-effect snow is notorious in upstate New York. Areas around Buffalo routinely get blasted with snowfall by the foot during arctic outbreaks.

Recipe for Lake-Effect Snow:

NOAA sums up lake-effect below.

"Lake-effect snow forms in the winter when cold air masses move over warmer lake waters. As the warm lake water heats the bottom layer of air, lake moisture evaporates into the cold air. Since warm air is lighter and less dense than cold air, it rises and begins to cool. The moisture that evaporates into the air condenses and forms clouds, and snow begins falling.

Snow clouds most often form in narrow bands where the size and orientation are determined by the shape of the body of water and the prevailing wind direction. In the most extreme cases, the heaviest bands of snowfall may be 20 to 30 miles wide and extend over 100 miles inland from the lake.

Within the band, snowfall rates may exceed 5 inches an hour and be accompanied by lightning and thunder, a phenomenon known as thundersnow. A band of snow can hover over one location for several hours, dropping several feet of snow; however, 10 to 15 miles on either side of that narrow band skies may be sunny with no snow at all.

Lake-effect snows are not confined to the Great Lakes region, although they are most common and heaviest there. Any large body of water can generate lake-effect snow downwind if it remains free of ice. The Great Salt Lake in Utah produces significant lake-effect snow. There's also bay-effect snow that forms in the same manner as lake-effect snow, only over the ocean. Cape Cod Bay in Massachusetts and Chesapeake Bay in Maryland and Virginia will occasionally produce bay-effect snow."

If you're not a fan of 4 feet of snow on your roof, be thankful we live "upwind" from the Great Lakes and the bulk the of lake-effect snow machine.

PH