How do the conditions for a tornado differ from the conditions for a hurricane?

Answer 1

To star off we must consider what the conditions for hurricanes and tornadoes have in common. To start, they both need conditions that strongly favor the formation of thunderstorms. Such conditions include plentiful warm, moist air to fuel the storms, a fairly rapid temperature drop with increasing altitude to destabilize the atmosphere, and a bit of low pressure to nudge the air upward and trigger the process. From here the conditions needed are different.

Hurricanes require so much moisture that they can only form over warm ocean water. They generally start from a weak, disorganized area of low pressure called a tropical disturbance which becomes stronger and more organized as it feeds on warm, moist air. Being tropical in nature, hurricanes are not associated with weather fronts. Partly because of the small temperature contrasts, the individual storm cells that make up a hurricane are usually fairly weak, but they combine to form a system that is greater than the sum of its parts. To sustain themselves, hurricanes need a continuous supply or warm, moist air. Dry air can cause a hurricane to weaken and dissipate while cold air will cause one to change into another kind of storm called and extratropical cyclone. Finally, to maintain their organized structure there needs to be little or no wind shear. In other words, the speed and direction of wind at different altitudes must be fairly uniform. Strong wind shear can essentially tear a hurricane apart.

In contrast to the relatively weak thunderstorms that make up hurricanes, tornadoes usually require very strong thunderstorms in order to form. As a result, while hurricanes form in the tropics, tornadoes usually form in temperate latitudes where there are larger contrasts in temperature and humidity. The storms that produce tornadoes most often form along a cold front or dry line where, respectively, cool or air or dry air collides with warm, moist air. Such collisions are not absolutely necessary, but they do create the most favorable conditions for tornadoes. The next ingredient needed is strong wind shear, which enhances the strength of individual storm cells and gives them the small-scale rotation they need to produce tornadoes.