What causes severe weather?

Powerful storms such as thunderstorms, hurricanes, and tornadoes are generated when warm, light air rises quickly into higher, colder air. This rising takes place in an unstable updraft that can reach over 100 miles per hour! Each type of powerful storm forms under specific conditions. (For example, hurricanes occur over moisture-rich oceans and coastlines. They draw their energy from warm ocean waters.) Understanding the conditions that allow powerful storms to develop is the key to weather preparedness.

Thunder and lightning

At any given moment, there are an estimated 2,000 thunderstorms in progress. These storms can vary from mild rainstorms to very damaging storms featuring hail and high winds. As stated above, thunderstorms form when warm air rises from Earth’s surface and moves upwards quickly into the colder levels of the atmosphere.

Thunder is simply the noise lightning makes as it travels through the air. Lightning occurs during all thunderstorms (though not every time it rains). Lightning causes billions of dollars in damage each year.

So what causes lightning? The updrafts of air in a storm carry water droplets, which have an electrical charge. These droplets are carried upward to heights where some freeze into ice and snow particles, forming a cloud. As these particles begin to fall back to Earth, electrical charges within the cloud become mixed. The differences in charge are released as lightning.

Since light travels faster than sound, you’ll see lightning before you hear its sound, thunder. The time lapse between the lightning and thunder differs, depending on how far away the storm is.

Spinning air: Tornadoes and Hurricanes

Both tornadoes and hurricanes are spinning columns of air capable of causing great damage. But there are differences between these two powerful storms. Tornadoes are more localized and typically found on land, while hurricanes can cover massive areas and draw their power from the warm tropical oceans.

Tornadoes range from only a few feet to one mile in diameter and normally only last a few minutes. Tornadoes are localized, but they can be extremely violent. The wind speed inside a tornado’s funnel can exceed 200 miles per hour. At such speeds, everyday objects turn into deadly projectiles. Because of this, tornado warnings should always be taken with the utmost seriousness. Tornadoes occur all over the world, at every time of the year, but they are most common in the spring and summer in the midwestern United States. This region’s propensity for tornadoes has earned it the name Tornado Alley.

Tornadoes form from thunderstorms, though not all thunderstorms generate tornadoes. The rising warm air of a thunderstorm can start to rotate because of changing wind directions at or near the ground. When the changing winds are caught in the updraft, the air rotation switches from horizontal (side to side) to vertical (up and down), creating conditions in which a funnel can develop. If conditions are right and the funnel does develop, it can extend to the ground, forming a tornado.

Weather forecasters can identify the cloud features and conditions that normally precede tornadoes, and they know where they are most likely to occur. However, predicting the exact time, location, and intensity of tornadoes is still very difficult.

While tornadoes threaten areas the size of towns or counties, hurricanes can threaten thousands of miles. These large storms can last for days or weeks. Hurricanes draw their strength from the warm tropical waters of the ocean. Unlike tornadoes, they lose their power source when they leave the ocean. Once on land, they gradually dissipate. This is why coastal areas typically see the strongest devastation from a hurricane, where it is at its strongest.

 

(adapted from source)