Query: How many days a year does the temperature in Detroit drop below 0?
Context: Detroit and the rest of southeastern Michigan have a humid continental climate (Köppen Dfa) which is influenced by the Great Lakes; the city and close-in suburbs are part of USDA Hardiness zone 6b, with farther-out northern and western suburbs generally falling in zone 6a. Winters are cold, with moderate snowfall and temperatures not rising above freezing on an average 44 days annually, while dropping to or below 0 °F (−18 °C) on an average 4.4 days a year; summers are warm to hot with temperatures exceeding 90 °F (32 °C) on 12 days. The warm season runs from May to September.