The energy that will instigate the storm is over the Pacific Northwest. Radar maps are quiet, but that will change by late Friday afternoon as the system gathers strength over Montana. Northern stretches of South Dakota are first in line, where a narrow band of three to four inches could fall from the Cheyenne River Reservation east toward Watertown. Aberdeen will likely be on the north side of a steep snowfall gradient, so forecast uncertainty there is moderate to high.

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A winter storm watch has been issued for parts of southern Minnesota and Wisconsin, as well as northern Iowa.

“Total snow accumulations of four to nine inches are possible,” the National Weather Service wrote in regard to Iowa, where winds are expected to gust near 35 mph. During the height of the storm, snowfall rates could approach one to two inches per hour.

In southern Minnesota, the three-to-four-inch swath will continue well south of Minneapolis before the storm really ramps up in Wisconsin. A widespread five to six inches with locally higher amounts is a good bet along the Wisconsin River east into Madison. A little less will come down in Milwaukee, but that city is still in line for a big dose of winter.

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Chicago could see rain mix with snow as colder air drains into the system from the north. While temperatures won’t drop to freezing, a few flakes could snake their way to ground level after sunset. The National Weather Service is calling for “less than a half inch of accumulation.” Some uncertainty in this area means higher totals are possible.

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“There’s some model output showing a bit more if the heavy snow band shifts south,” said Ricky Castro, a meteorologist at the National Weather Service office in Chicago. “There’s definitely wiggle room.”

The final position of the snow band will determine how much falls in the Windy City. While April snow in Chicago isn’t unheard of, totals pushing an inch are unusual.

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“The latest one-inch-plus snowfall was 1.3 inches on May 3, 1907,” Castro said. “May 1, 1940, also had 1.6 inches.”

Castro noted that there’s an outside chance Chicago’s O’Hare International Airport — the city’s official climate site — could top one inch if a heavy snow band stalls or meanders south. How likely is this to occur? “It’s in the realm of possibility,” Castro said.

Earlier this month, Chicago picked up a surprise 5.4 inches on April 14, its second latest five-inch-plus snowfall. The upcoming event could be an overachiever. And like last time, the quick burst of snow may overwhelm the comparatively warm pavement/surface temperatures, allowing the snow to accumulate more quickly than it can melt.

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Detroit, too, will see a brief blitz of wintry mischief from the quick-hitting storm. Despite highs in the 60s with a chance of thunderstorms Friday, temperatures plummeting into the 30s Saturday night will bring about an inch of snow. The system will eventually dissipate as it drops a few more flurries over Upstate New York and Vermont before being absorbed into a large system in Canada.