Three types of airmasses in which tornadoes form are identified from consideration of 286 representative soundings and a median sounding for each type presented and discussed. Previously published descriptions of tornadic airmasses are identified as being of TYPE I, the most common TYPE, and some refinement is given. Two other TYPES are described and it is contended that all tornadoes and water spouts of the continental United States and adjacent waters form in airmasses that fit one of the three classifications. Finally, the weather phenomena that most commonly accompany tornadoes in each TYPE of airmass are described and related to the height of the wet-bulb freezing level above the terrain.

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