1.) What makes them? Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. These thunderstorms often produce large hail, strong winds, and tornadoes. Tornadoes in the winter and early spring are often associated with strong, frontal systems that form in the Central States and move east. Occasionally, large outbreaks of tornadoes occur with this type of weather pattern.

2.) How many are reported nationwide per yer? The "average" over the past 30 years has been around 800 per year. In those 30 years however the lowest amount reported was 653 in 1987 and the most being 1258 in 1992.

3.) What time of day do they usually happen? Tornadoes are most likely to occur between 3 p.m. and 9 p.m. but have been known to occur at ALL hours of the day or night.

Hope that helps you!