Snow storm slams U.S. Plains, heads for Northeast

Traffic makes its way with limited visibility on interstate highway I-635 during a blizzard that covered the metro area in Kansas City, Kansas, February 4, 2014. REUTERS/Dave Kaup

KANSAS CITY, Missouri (Reuters) - An unusually heavy winter storm slammed into the nation's mid-section Tuesday, heading east and threatening roughly two-thirds of the country with what forecasters said could be up to a foot (30 cm) of snow.

The storm system forced the closing of many state offices and schools in hardest-hit Kansas, where Governor Sam Brownback declared a state of "disaster emergency."