Cold Canadian air swept deep into the Midwest, sending temperatures plummeting 20 to 30 degrees lower than normal through the Missouri Valley and into the Texas and Oklahoma panhandles. Record lows chilled South Dakota and Montana, and up to an inch of snow fell across most of Nebraska and southern Iowa, with Kansas City and Kirksville, Mo., getting sleet. Cities reporting record lows included Billings, Mont., 21; Havre, Mont., 11, and Sioux Falls, S.D., 18. Huron, S.D., tied a previous record low of 15 degrees. The cold front brought scattered thunderstorms from upstate New York through northern Texas. The heaviest rain fell across southern Illinois and southeastern Missouri.