Beginning on the evening of December 10, a remarkable congeries of tornadoes struck six states of the United States. December is late in the year for a tornado — they become less likely as weather cools. But these tornadoes were undeterred by the calendar and struck to disastrous effect in some highly populated areas.
The science of tornadoes is well established in its broad outlines, although the field retains some mystery.
Atmospheric instability is key to the development of a tornado. This takes the form of warm moist air near the ground, with cooler dry air aloft, and wind shear. such an airmass promotes the development of a strong updraft, and the windshear, while increasing the strength of the updraft, can also promote the rotation which is so distinctive to tornadoes.
Strange New Worlds:
Predicting tornadoes, and providing people along a potential storm track with more than about fifteen minutes of warning, is proving to be a great challenge for meteorologists. It is not a macro event like a hurricane. There are lots of processes at very small scales that very much matter to whether a tornado will form or how intense it will be if it does. One expert recently said that he and his fellow specialists are “still sort of trying to wrap our heads around” the level of complexity involved.