The Upper Midwest remains locked in the deep freeze, with bitter temperatures stretching into a fourth day across several states. The cold snap arrived Saturday night as waves of Arctic air swept south from Canada, pushing temperatures to dangerous lows and leaving a section of the country well-versed in winter's pains reeling. Authorities suspect exposure has played a role in at least four deaths so far. Among the coldest temperatures recorded Tuesday was 35 below at Crane Lake, Minn., a National Weather Service forecaster said early Wednesday. The coldest location in the lower 48 states Monday was Embarrass, Minn., at 36 below, according to the National Weather Service. The bitter conditions were expected to persist into the weekend in the Midwest through the eastern half of the U.S.