Water evaporates from the surface of the earth. Warm air saturated with water vapor rises. As this happens, the air cools because the higher we get above the ground, the colder it becomes. It is noticeable when you look at mountains. Their peaks are snow-covered, while the areas at the foot of the mountain are still warm. At a higher altitude, the water vapor turns into a fog that is tiny droplets of water. Now clouds of different shapes are formed from the fog.
For a thunderstorm to appear, there should be a separation of the electric charge. Large and heavy cloud particles usually have a negative charge. Also, Large and heavy cloud particles fall faster. The charge in the cloud separates, creating an electric voltage. It causes lightning. It is an electrical discharge, more precisely an electric spark of enormous size.
What is a thunderstorm?
Thunderstorms are one of those phenomena caused essentially by differences in temperature, pressure, and so on. The bigger the differences there are, the more severe those thunderstorms are. A big gradient temperature causes winds and the movement of air masses.
Thunderstorms come in a variety of shapes and sizes. They can end up looking like big clumps of cauliflower as they run out of moisture before they reach the top of the troposphere. Also, They tend to spread outward if they reach the stratosphere, forming that characteristic flat and Ville-shaped top of a cumulonimbus cloud. They can occur individually and cluster together or form up into squall lines given enough heat and humidity. Also, they can grow into immense rotating supercells. Then there are the notorious mesoscale convective complexes.
Squall lines that can form one day persist late into the night with heavy rain, hail, and possibly tornadoes before dying down by morning. And then kick up again into another line of powerful thunderstorms by afternoon. Larger thunderstorms can even produce such strong gusts of wind flowing out from underneath them that these gusts can form squall lines of their own. These are known as Derechos. Storm formation can grind to a halt with just one simple addition to the whole scenario.
How does a thunderstorm form?
How do thunderstorms form? It’s a difference in atmospheric gradient temperatures. When you have a cold and hot they don’t like each other. So they start swirling around and then rising into the atmosphere. And that’s what we call convection that creates clouds. The further that warm air rises in the atmosphere, the more it will condense. Eventually, precipitate in the form of some rain. So this is an early stage in the cumulus stage.
The clouds need to be very large to get rain with thunderstorms. Such clouds are called cumulus. It is so cold that the water zone begins to freeze, and ice crystals form at the cloud’s top. These crystals start to fall and become the Centers of forming large drops of water that move down. It means that large drops are already flying down, and rain will soon pour out of the cloud.
The cloud begins to build high 10-15 thousand feet into the air. Then that precipitation starts the fall. But there’s an issue here. Sometimes storms can overgrow over a short amount of time and become 45 or 50 thousand feet tall, where jumbo jets usually fly. The typical airplanes that you see overhead and you get supercell thunderstorms.
They also have a graphic depicting that in just a moment. Eventually, the thunderstorm will exhaust itself. It will run out of energy for updrafts and downdrafts. So the heavy rain comes in the mature stage and thunderstorm development.
There are 3 things to form a thunderstorm:
- A source of moisture.
- An unstable atmosphere.
- Mechanism to trigger storm.
Remember this acronym limb, lift, instability and moisture. Lift is that convection with the warm air rising into the atmosphere creating the conditions needed for thunderstorms.
Instability is directly related to lifting once that air is up in the atmosphere and condenses it. It creates the clouds and eventually that turbulent weather.
The moisture out over the ocean is typically good for tropical systems, just a basic thunderstorm cluster.
How does a puffy white cumulus cloud turn into an immense tower and cumulonimbus that can deliver powerful winds dousing rainfall, even hail, and tornadoes? To answer this question, let’s isolate one warm, humid blob of air as it rises as long as the blob is warmer than its surroundings. It rises, expands due to the lower pressure, and cools due to that expansion until it reaches the same temperature.
If the blob’s temperature drops to the dewpoint, water vapor will condense out of it, and a cloud will form. And this condensation begins a cycle that drives the growth of the cloud. It is because when water vapor condenses, it releases heat. As soon as the cloud forms, the condensation gives the block back, and some heat will lose due to expansion. Because the warmer air holds more moisture, the blob recovers some of the water vapor it lost as well.
When all that is done, the blob is still warmer than its surroundings, so it rises, and the whole thing starts all over again like expansion, cooling, condensation, recovery of heat, and water vapor. And it rises again. This keeps happening over and over and over until the blob runs out of water vapor.
So when it’s hot and sticky out, the abundant heat gives a blob of air a strong impulse to rise. The humidity provides a lot of water vapor to drive the growth of the clouds. Without anything to stop the process, this can produce clouds that can climb to the stratosphere.
Now expand all of this out, and we say that’s not just one blob of air rising to make the cloud. But an ever-flowing conveyor of them drawing a constant supply of warm, humid air up into the developing cloud in the form of powerful winds known as updrafts. When the rain starts to fall from the clouds, this reduces downdrafts.
And the storm can persist for some time like this. Especially if strong upper-level winds caused the cloud to become tilted, which separates the updrafts and downdrafts enough, they wouldn’t cancel each other. During the storm’s mature phase, it’s at this point that you will see abundant lightning and the possibility of hail and even tornadoes.
A layer of warm air higher up above the ground, a typical temperature profile of the atmosphere, gets cooler the higher you go. Meteorologists call the presence of this warm layer a temperature inversion. Above the inversion, the normal temperature profile takes over. Forecasters and storm chasers often refer to this as the airmass being capped. This cap is most commonly associated with warm air riding up over cooler, denser air near a warm front.
Or if there’s a warm, stagnant airmass stuck over a region. The air closest to the ground will cool overnight. But this cooling may not reach the air higher up before sunrise. As rising air reaches the cap, more warm, humid air parcels become trapped by this cap blocked from reaching the cooler air above it. This causes a buildup of instability across this warm layer and frustration for storm chasers because this entire scenario will prevent storms from developing.
However, if conditions can break the cap, the air beneath it warms up enough to cancel out the inversion, Some powerful convection bursts past it. The sudden upward rush of warm, humid air causes explosive cloud development. And a sudden rush of storm chasers to their vehicles as this often results in severe thunderstorms.
Different types of thunderstorms
Scientists have classified thunderstorms into four categories:
1. Single-cell: Single cells are the pop-up thunderstorms you may see on a warm summer afternoon. They are caused by the ground’s heating, which heats the air above and causes air to rise. These thunderstorms may produce brief rain, minor hail, and some lightning but typically don’t last more than twenty to thirty minutes before dissipating.
2. Training thunderstorms: Training thunderstorms occur when individual cells line up one behind the other. It occurs when one cell matures, and air currents create a new cell behind it. There are usually multiple cells in various stages of development, but they all follow the same path. These storms can produce large amounts of rainfall and may also have some hail, lightning, and possibly a weak tornado.
3. Squall lines: Squall lines are long individual cells lined up side by side. These can be associated with an advancing strong cold front. A strong rush of wind ahead of a squall line may be present called a gust front. A gust front may have powerful winds, with wind speeds up sixty miles per hour or more. These storms can produce brief heavy rain, lots of lightning, hail, and tornadoes.
4. Supercells: A supercell is a large, rotating storm. One cell may be up to 15 miles in width. Supercell storms often occur along a dry line, a boundary between hot, dry air and warm moist air. These two air masses may get squeezed together, causing the hot, dry air to override the warm moist air, which stops the warm moist air from rising. If the two air masses are further pushed together, the warm moist air may push through the hot, dry air, rising rapidly. This rising air may develop a rotation through areas where the surrounding winds move in different directions.
Once these conditions are in place, a supercell may last for hours and move hundreds of miles. Supercells produce lots of rain and lightning, large hail, and may produce very strong tornadoes. Supercell storms are more common in the Great Plains area of the United States, although they can occur in many other US locations.
It’s essential to know about safety during a thunderstorm. Usually, lightning strikes high objects. Therefore, you shouldn’t hide from the rain under a tree during a thunderstorm. It is dangerous to be in the water or even near any water body during a thunderstorm as water conducts an electric current.
Did you notice that we always see lightning first during a thunderstorm, and only after that do we hear the thunder? This is because the lightning’s light reaches us almost instantly since the light’s speed is very fast. Thunder is a sound whose speed is much slower, so the thunder reaches us with a delay.
“Thunderstorms, UCAR Center for Science Education.
National Severe Storms Laboratory. “SEVERE WEATHER 101 / Thunderstorm Basics”. SEVERE WEATHER 101. National Oceanic and Atmospheric Administration.
Yikne Deng. Ancient Chinese Inventions. Chinese International Press.