SIOUX FALLS, S.D. (AP) – Temperatures crashed to record lows well below zero Monday as a huge mass of arctic air blustered southward across the Midwest and West, keeping people indoors and leading some cities to open shelters.

The cold and remnants of the weekend blizzard that accompanied it closed hundreds of schools from the northern Plains to the Great Lakes states.

Major highways in Minnesota, and North and South Dakota reopened after Sunday’s blizzard dropped as much as 14 inches of snow, but hundreds of schools were closed in the three states.

Record lows Monday included 19 below zero in Denver, where the previous Dec. 15 record of minus 6 was set in 1951; and minus 16 at Sidney, Neb.