March Madness: Downpours, thunder, North Shore snow

Beware the Ides of March indeed.

Things are getting a little crazy on the weather maps over Minnesota today. An unseasonably warm March low pressure storm is winding up and cranking out some unusual weather for mid-March in the Upper Midwest. Watch the system deepen and stall over the western Great Lakes.

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NOAA

Rare March lightning strikes

The first waves of rain and thunderstorms stretch from eastern Iowa all the way north through Minnesota to Winnipeg, Manitoba. I can't recall seeing lightning strikes as far north as Winnipeg in mid-March.

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LightningMaps.org

Heavy rain potential

As the system deepens and pulls in more moisture from the south, some fairly incredible multi-inch rainfall totals could fall from the Twin Cities eastward to Eau Claire, Wis., and from La Crosse, Wis., to Duluth and the Iron Range.

The National Oceanic and Atmospheric Administration's NAM 4 km model shows the intense low pressure system wrapping rain bands in, then changing precipitation to snow as colder air works into the system. Some metro slush is possible by Thursday morning.

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NOAA via College of Dupage

Widespread 1- to 2-inch rainfall totals, with a 2 to 4 inches-plus bull's-eye look likely to set up over eastern Minnesota and western Wisconsin as the storm spins in place near Green Bay.

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Heavy snow north

Rain changes to snow in the 218 area code late tonight into Wednesday. Winter storm watches have been expanded and now cover most of northern Minnesota and Wisconsin.

If the rain changes to snow as expected tonight into Wednesday, heavy snowfall totals will blast the Arrowhead and North Shore communities. The Duluth National Weather Service office paints the potential for up to a foot of snow for the North Shore.

No, winter is not over up north.

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Duluth NWS

Severe risk south

The risk for a severe outbreak is there today from eastern Iowa and Missouri through Illinois and Indiana.

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NOAA

March reality check

I know many of us are tempted to jump start the season and plant a few petunias. The wise will wait a little longer. Expect a few more sub-freezing nights this week.

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Weatherspark ECMWF data

I still think this will be a longer than average growing season, but the last 32-degree temp in the metro in spring is April 29, not March 15.

Those Supertunias can wait a little longer to be safe.

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Sketchy ice on Excelsior Bay of Lake Minnetonka this morning. Image: Maynard's web cam.

Ice out already

Many of the smaller lakes in the Twin Cities and southern Minnesota are now ice free. Some of those are record early ice out dates.

I expect the rain and wind will take out the bigger metro lakes like Minnetonka, Calhoun, Harriet, Nokomis and White Bear today or tomorrow. Check the list here at the Minnesota Department of Natural Resources.

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Minnesota DNR

Here's a great explainer on the physical process for ice out in Minnesota in spring.

How Lake Ice Melts

A wonderful description of how lake ice melts away appeared on the web blog "Air Mass", hosted by the Star Tribune's Bill McAuliffe. Ed Swain, of the Minnesota Pollution Control Agency describes the process of freezing and thawing lakes.

  • In the late fall, the lake loses heat to the atmosphere, and then on a day or night when the wind is not blowing, ice forms. The ice gets thicker as long as the lake can continue to lose heat.

  • In most Januaries and Februaries, snow both reflects sunlight and insulates the lake. With a thick snow layer, the lake neither gains nor loses heat. The bottom sediment is actually heating the lake water slightly over the winter, from stored summer heat.

  • Around March, as the air warms and the sun gets more intense, the snow melts, allowing light to penetrate the ice. Because the ice acts like the glass in a greenhouse, the water beneath it begins to warm, and the ice begins to melt FROM THE BOTTOM.

  • When the ice thickness erodes to between 4 and 12 inches, it transforms into long vertical crystals called "candles." These conduct light even better, so the ice starts to look black, because it is not reflecting much sunlight.

  • Warming continues because the light energy is being transferred to the water below the ice. Meltwater fills in between the crystals, which begin breaking apart. The surface appears grayish as the ice reflects a bit more light than before.

  • The wind comes up, and breaks the surface apart. The candles will often be blown to one side of the lake, making a tinkling sound as they knock against one another, and piling up on the shore. In hours, a sparkling blue lake, once again!