all that were servers were william gallus is a professor of meteorology and i was state university uses the path of destruction left by the tornadoes to be the longest ever. recorded tornadoes form on any day where you have strong wind shear, which means the winds are changing. their speed and direction as you go up in the atmosphere. so on friday night we had very strong values of wind shear in the atmosphere, which is pretty typical in winter. but the other ingredient we need is instability, or a lot of energy that is supplied by having warm and humid conditions near the ground that is often lacking in the winter. but as you heard in this event, there is spring like warped and humidity presence in this region to those 2 ingredients come together and allow for thunderstorms to begin to rotate. and the strong upward motion in the thunderstorm can concentrate the rotation to make it a spin very fast helping to form for nato's. we've gone 8 years in the united states since we've had an f 5 tornado, which should be the maximum strength tornado. they have not yet rated this very long track

how many, thanks. indeed, william gallus is a professor of meteorology at iowa state university. he joins us now from ames of the state and for i will professor good to have you with us. let's start with some science. how and why do tornadoes form? tornadoes form on any day where you have strong wind shear, which means the winds are changing their speed and direction as you go up in the atmosphere. so on friday night we had very strong values of wind shear in the atmosphere, which is pretty typical in winter. but the other ingredient we need is instability or a lot of energy that is supplied by having warm and humid conditions near the ground . that is often lacking in the winter, but as you heard in this event, there is spring like warmth and humidity present in this region to those 2 ingredients come together and allow for thunderstorms to begin to rotate. and the strong upward motion in the thunderstorm can concentrate rotation to make it a spin very fast helping to form for nato's when these were ferocious tornadoes. is that particularly unusual? i mean, in terms of the size