‘What about those crazy forecast maps with 20”+ of snow!?’ Forecasts uncertain as major winter storm approaches Chicago area

A major winter storm is expected to hit Chicago Tuesday night and could dump a half-foot or more of snow before it moves out sometime Thursday morning.

It’s not clear exactly how much snow will fall. The National Weather Service estimates at least 6 inches in the Chicago area and 8-10 inches to the south and in Indiana.

Some computer models show as much as 20 inches of snow, though the weather service issued a caution about that forecast.

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“What about those crazy forecast maps with 20”+ of snow!?” the weather service tweeted. “Raw model snowfall amounts appear too high since they don’t account for compaction over the 48 hours of the snow. Will some areas see double-digit snow totals? Probably. But 20” seems unlikely at this time.”

Still, the weather service has issued a winter weather watch from Tuesday evening through Thursday morning for central and southern Cook County, north and southern and eastern Will County, Kankakee County, Grundy County and, in Indiana, Lake and Porter counties.

The storm will hit in “two punches,” one late Tuesday through early Wednesday, the other Wednesday night through early Thursday, according to the weather service.

“It may not actually stop snowing on Wednesday,” said Casey Sullivan, a meteorologist with the weather service. “It will probably just lighten up.”

The second wave will likely be followed by lake effect snow, though Sullivan emphasized the uncertainty of the forecasts, especially for the second wave.

The storm will move from the south, crossing Peoria and Bloomington and Kankakee and then heading into Indiana. The heaviest bands of snow are to the south of the city and in Indiana, he said.

“That looks really solid,” he said.

Monday is the 11th anniversary of the Groundhog Day blizzard, which buried the Chicago area under more than 20 inches of snow, the third largest snowstorm on record for the city.

Winds of 60 mph and higher whipped up drifts 2 to 5 feet high, 10 feet in some places. There was also lightning and thunder and hail.

Sullivan said blizzard conditions are not expected in the storm that is approaching.

“We’re not expecting the wind with this system like then,” he said. “Nothing close to blizzard conditions.”