Temperatures are 10 to 20 degrees (Fahrenheit) below normal in the frigid front that moved in last week and was expected to last through the weekend, he said.

The big chill is roaring in from "the Arctic door wide open," he said. Relief should come by early or mid-week next week when the air flows shift, bringing in warmer air from the Pacific.

Temperatures this winter, though unseasonably cold, are "not record-breaking," he said.

The harshest cold weather on Wednesday was in the states of Minnesota, Wisconsin, Iowa and Illinois, he said.

Lake-effect snow, produced by cold air blowing over the warmer Great Lakes, had dumped "big snows," he said.

In Oswego, New York, lake-effect snow was expected to drop between six to 10 inches (15-25 centimeters) during the day. CNN television network reported that 62 inches (158 centimeters) had fallen in the past five days in the city on the eastern end of Lake Ontario.

In Chicago, a high temperature of near 15 degrees F (minus nine Celsius) was forecast, with a wind-chill factor bringing it to between minus five and zero.

The Windy City, on the shores of Lake Michigan, saw scores of road accidents -- from fender-benders to 30-vehicle pileups -- Tuesday on slick roads, the Chicago Tribune newspaper reported. At least one death was attributed to icy roads.

The influence on the US of a moderately strong El Nino, which had an unusual warm winter in many states, has weakened in the last few weeks, he said.

El Nino is an occasional seasonal warming of the central and eastern Pacific Ocean that upsets normal weather patterns from the western seaboard of Latin America to East Africa, and potentially has a global impact on climate.

El Nino was expected to play only a marginal role in US weather by March and April, Feltgen said.

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