Although favorable conditions for tornadoes in the United States can occur at any time, they are most common in spring and least common in winter. Because spring is a transitional period for the climate, there are more chances of cooler air meeting with warmer air, resulting in more thunderstorms.
linear. 1  of or relating to a line or lines. 2  made of or using lines: linear design. 3  in relation to length only; extended in a line.  designating or of a style of art in which forms are sharply delineated and line is emphasized over color, light and shadow, etc.
spiral (plural spirals) ( 1 geometry) A curve that is the locus of a point that rotates about a fixed point while continuously increasing its distance from that point. ( 2 informal) A helix. 3  A self-sustaining process with a lot of momentum involved, so it is difficult to accelerate or stop it at once.