Cross-section of a supercell
| The most damaging tornadoes form in "supercells", large rotating towering storm centers. The standard explanation, "warm moist Gulf air meets cold Canadian air and dry air from the Rockies", although generally true, is an oversimplification. Many thunderstorms form under those conditions: where a cold front meets warm moist air near a "dryline" - a sharp change in humitity. But not all thunderstorms produce tornadoes, even when the large-scale environment is extremely favorable for tornadic thunderstorms. Monitoring these storms with Doppler Radar helps forecasters to know whether the storm cells have a strong circulating winds. Supercells often also have damaging hail. |
Credit: Storm Prediction Center
For more info: http://www.spc.noaa.gov/faq/tornado/