As the downdraft becomes stronger, it eventually overtakes the updraft, leading to the thunderstorm's demise. If that warm, moist air can no longer rise, the entire process stops and what once was a dangerous storm, becomes a cloud with light rain that gradually dissipates. Now that we understand the life cycle of storms, let's break down the four different types they can become:.
A textbook, run of the mill single storm that develops, grows, and dies like described above would be classified as a single-cell thunderstorm. You may have heard a meteorologist refer to these as "popcorn" or "pop-up" storms.
They are commonly found in the spring and summer, and can bring brief periods of heavy rain and hail. While these storms can be severe, depending on the instability, many times they are not and can bring a welcome relief to intense summertime heat.
While these storms can contain the usual suspects, like hail and gusty winds, the threat of flooding is greater with these. Multi-cell thunderstorms can line up and move continuously over the same area, dumping significant amounts of rain.
This is called "training" and often leads to flash flooding. There have been instances where multi-cell thunderstorms dump more than 5" of rain in an area in just an hour or two!
For a tornado to form, there also needs to be spinning air near the ground. This happens when air in the storm sinks to the ground and spreads out across the land in gusts. Gusts of warmer air rise as they blow. Gusts of cooler air sink as they blow across the land. If there are enough rising and sinking gusts, the air near the ground starts spinning. They form so fast that each new cell develops further and further upstream giving the appearance of the thunderstorm cluster is stationary or is moving backwards, against the upper level wind.
Tremendous rainfall amounts can be produced over very small areas by back-building thunderstorms. In , 15" mm fell in six hours over parts of Rapid City, SD due to back-building storms. Sometimes thunderstorms will form in a line which can extend laterally for hundreds of miles. These "squall lines" can persist for many hours and produce damaging winds and hail. Updrafts, and therefore new cells, continually re-form at leading edge of system with rain and hail following behind.
Individual thunderstorm updrafts and downdrafts along the line can become quite strong, resulting in episodes of large hail and strong outflow winds which move rapidly ahead of system. While tornadoes occasionally form on the leading edge of squall lines they primarily produce "straight-line" wind damage.
This is damage as a result of the force of the down draft from a thunderstorm spreading horizontally as it reaches the earth's surface. Long-lived strong squall lines after called "derechos" Spanish for 'straight'. Derechos can travel many hundreds of miles and can produce considerable widespread damage from wind and hail. Learn more about derechos.
Often along the leading edge of the squall line is a low hanging arc of cloudiness called the shelf cloud. This appearance is a result of the rain cooled air spreading out from underneath the squall line acts as a mini cold front.
All these conditions can result in rolling, spinning air currents inside the cloud. Although this spinning column of air starts out horizontal, it can easily go vertical and drop down out of the cloud. When it touches the ground, it's a tornado. The winds inside the spinning column of some tornadoes are the fastest of any on Earth. They have been clocked at over miles per hour! Sometimes the spinning column of air lifts off the ground, then touches down again some distance along its path.
It's hard to measure the winds in a tornado directly. So they are evaluated by the amount of damage they do. Here is a scale meteorologists use to describe tornado intensity based on damage. These satellites can more quickly monitor the motion of clouds to identify a severe storm as soon as it develops.
They are also better at understanding what's actually going on inside the cloud: what characteristics the cloud has that indicate a severe storm and how much lightning it produces.
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