Tornadoes don’t just happen in the spring. Decades of NOAA data shows every fall and winter month still averages dozens of tornadoes nationwide. November's tornado threat is greatest across the Deep South, especially the lower Mississippi Valley, as Gulf moisture collides with strengthening cold fronts. Nighttime tornadoes become more common in these colder months too, and they're more than twice as likely to be deadly as tornadoes that strike during the day.