(CNN) A complex storm system is gaining strength over the Midwest as two storms will combine to dump snow from Missouri to Maine this week.

"A strong winter storm will bring the heaviest snow from the Great Lakes into New England, including cities like Chicago, Detroit, and Buffalo," said CNN meteorologist Dave Hennen.

There are more than 20 million people under winter storm alerts issued by the National Weather Service.

Monday's forecast models were predicting significant snow for Chicago. Forecasts now call for the snow band to setup farther south, leaving the city with far less snow than initially predicted.

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