The airplane basically needs winds flowing under and over the wing for it to fly. When that wind or air changes direction, or doesn't flow in that direction, then it causes problems.

With downbursts, they can be as damaging or as destructive as tornadoes.

Barry Gooden

The sirens are an outdoor warning system. They're not effective late at night when most people are indoors asleep. And because of atmospheric conditions, tornadoes are more likely to form at night.

Barry Gooden