Welcome to the I Can't Sleep Podcast,
Where I help you drift off one fact at a time.
I'm your host Benjamin Boster,
And today's episode is about thunderstorms.
A thunderstorm,
Also known as an electrical storm or a lightning storm,
Is a storm characterized by the presence of lightning and thunder.
Relatively weak thunderstorms are sometimes called thundershowers.
Thunderstorms occur in cumulonimbus clouds.
They are usually accompanied by strong winds,
And often produce heavy rain and sometimes snow,
Sleet,
Or hail.
But some thunderstorms can produce little or no precipitation at all.
Thunderstorms may line up in a series or become a rain band known as a squall line.
Strong or severe thunderstorms include some of the most dangerous weather phenomena,
Including large hail,
Strong winds,
And tornadoes.
Some of the most persistent severe thunderstorms,
Known as supercells,
Rotate,
As do cyclones.
While most thunderstorms move with the mean wind flows through the layer of the troposphere that they occupy,
Vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.
Thunderstorms result from the rapid upward movement of warm,
Moist air,
Sometimes along a front.
However,
Some kind of cloud forcing,
Whether it is a front,
Shortwave trough,
Or another system,
Is needed for the air to rapidly accelerate upward.
As the warm,
Moist air moves upward,
It cools,
Condenses,
And forms a cumulonimbus cloud that can reach heights of over 20 kilometers,
Or 12 miles.
As the rising air reaches its dew point temperature,
Water vapor condenses into water droplets or ice,
Reducing pressure locally within the thunderstorm cell.
Any precipitation falls the long distance through the clouds towards the Earth's surface.
As the droplets fall,
They collide with other droplets and become larger.
The falling droplets create a downdraft as it pulls cold air with it,
And this cold air spreads out at the Earth's surface,
Occasionally causing strong winds that are commonly associated with thunderstorms.
Thunderstorms can form and develop in any geographic location,
But most frequently within the mid-latitude,
Where warm,
Moist air from tropical latitudes collides with cooler air from polar latitudes.
Thunderstorms are responsible for the development and formation of many severe weather phenomena,
Which can be potentially hazardous.
Damage that results from thunderstorms is mainly inflicted by downburst winds,
Large hailstones,
And flash flooding caused by heavy precipitation.
Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.
There are three types of thunderstorms,
Single-cell,
Multi-cell,
And supercell.
Supercell thunderstorms are the strongest and most severe.
Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes.
Dry thunderstorms with no precipitation can cause the outbreak of wildfires from the heat generated from the cloud-to-ground lightning that accompanies them.
Several means are used to study thunderstorms,
Weather radar,
Weather stations,
And video photography.
Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century.
Beyond the Earth's atmosphere.
Thunderstorms have also been observed on the planets of Jupiter,
Saturn,
Neptune,
And probably Venus.
Warm air has a lower density than cool air,
So warmer air rises upwards and cooler air will settle at the bottom.
Clouds form when relatively warmer air carrying moisture rises within cooler air.
The moist air rises and as it does so,
It cools and some of the water vapor in that rising air condenses.
When the moisture condenses,
It releases energy known as latent heat of condensation,
Which allows the rising packet of air to cool less than the cooler surrounding air,
Continuing the cloud's ascension.
If enough instability is present in the atmosphere,
This process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder.
Meteorological indices such as convective available potential energy,
CAPE,
And the lifted index can be used to assist in determining potential upward vertical development of clouds.
Generally,
Thunderstorms require moisture,
An unstable air mass,
And a lifting force in order to form.
All thunderstorms,
Regardless of type,
Go through three stages.
The developing stage,
The mature stage,
And the dissipation stage.
The first stage of a thunderstorm is the cumulus stage,
Or developing stage.
During this stage,
Masses of moisture are lifted upwards into the atmosphere.
The trigger for this lift can be solar illumination,
Where the heating of the ground produces thermals,
Or where two winds converge,
Forcing air upwards,
Or where winds blow over terrain of increasing elevation.
The moisture carried upward cools into liquid droplets of water due to lower temperatures at high altitude,
Which appear as towering cumulus clouds.
As the water vapor condenses into liquid,
Latent heat is released,
Which warms the air,
Causing it to become less dense than the surrounding drier air.
The air then continues to rise in an updrought through the process of convection.
This process creates a low pressure zone within and beneath the forming thunderstorm.
In the mature stage of a thunderstorm,
The warmed air continues to rise until it reaches an area of warmer air and can rise no further.
Often this cap is the tropopause.
The air is instead forced to spread out,
Giving the storm a characteristic anvil shape.
The resulting cloud is called cumulonimbus incus.
The water droplets coalesce into larger and heavier droplets and freeze to become ice particles.
As these fall,
They melt to become rain.
If the updraft is strong enough,
The droplets are held aloft long enough to become so large that they do not melt completely,
But fall as hail.
While updrafts are still present,
The falling rain drags the surrounding air with it,
Creating downdrafts as well.
The simultaneous presence of both an updraft and a downdraft marks the mature stage of the storm and produces cumulonimbus clouds.
During this stage considerable internal turbulence can occur,
Which manifests as strong winds,
Severe lightning,
And even tornadoes.
Typically,
If there is little wind shear,
The storm will rapidly enter the dissipating stage and rain itself out.
But,
If there is sufficient change in wind speed or direction,
The downdraft will be separated from the updraft,
And the storm may become a supercell,
Where the mature stage can sustain itself for several hours.
In the dissipation stage,
The thunderstorm is dominated by the downdraft.
If atmospheric conditions do not support supercellular development,
This stage occurs rather quickly,
Approximately 20 to 30 minutes into the life of the thunderstorm.
The downdraft will push down out of the thunderstorm,
Hit the ground,
And spread out.
This phenomenon is known as a downburst.
The cool air carried to the ground by the downdraft cuts off the inflow of the thunderstorm.
The updraft disappears and the thunderstorm will dissipate.
Thunderstorms in an atmosphere with virtually no vertical wind shear weaken as soon as they send out an outflow boundary in all directions,
Which then quickly cuts off its inflow of relatively warm,
Moist air and kills the thunderstorm's further growth.
The downdraft hitting the ground creates an outflow boundary.
The stronger the outflow boundary is,
The stronger the resultant vertical wind shear becomes.
There are four main types of thunderstorms.
Single cell,
Multi-cell,
Squall line,
Also called multi-cell line,
And supercell.
Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere.
Wind shear.
Single-cell thunderstorms form in environments of low vertical wind shear and last only 20 to 30 minutes.
Organized thunderstorms and thunderstorm clusters,
Lines,
Can have long life cycles as they form in environments of significant vertical wind shear,
Normally greater than 25 knots or 13 meters per second in the lowest 6 kilometers or 3.
7 miles of the troposphere,
Which aids the development of stronger updrafts as well as various forms of severe weather.
The supercell is the strongest of the thunderstorms,
Most commonly associated with large hail,
High winds,
And tornado formation.
A single-cell thunderstorm,
Also known as an air-mass thunderstorm,
Is a single thunderstorm with one main updraft.
Single-cell thunderstorms are the typical summer thunderstorms in many temperate locales.
They also occur in the cool,
Unstable air that often follows the passage of a cold front from the sea during winter.
Within a cluster of thunderstorms,
The term cell refers to each separate principal updraft.
Thunderstorm cells occasionally form in isolation,
As the occurrence of one thunderstorm can develop an outflow boundary that sets up new thunderstorm development.
Such storms are rarely severe and are a result of local atmospheric instability.
Hence the term Airmass Thunderstorm.
Mature thunderstorms are found near the center of the cluster,
While dissipating thunderstorms exist on their downwind side.
Multicell storms form as clusters of storms,
But may then evolve into one or more squall lines.
While each cell of the cluster may only last 20 minutes,
The cluster itself may persist for hours at a time.
They often arise from convective updrafts in or near mountain ranges and linear weather boundaries,
Such as strong cold fronts or troughs of low pressure.
These types of storms are stronger than the single-cell storm,
Yet much weaker than the supercell storm.
Hazards with the multi-cell cluster include moderate-sized hail,
Flash flooding,
And weak tornadoes.
A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front.
The Squall Line contains heavy precipitation,
Hail,
Frequent lightning,
Strong straight-line winds,
And possibly tornadoes and waterspouts.
Severe weather,
In the form of strong,
Straight-line winds,
Can be expected in areas where the squall line itself is in the shape of a bow echo,
Within the portion of the line that bows out the most.
Some bow echoes in the summer are called directoes and move quite fast through large sections of territory.
Supercell storms are large,
Usually severe quasi-steady-state storms that form in an environment where wind speed or wind direction varies with height,
Wind shear.
And they have separate downdrafts and updrafts,
I.
E.
,
Where its associated precipitation is not falling through the updraft,
With a strong rotating updraft,
A mesocyclone.
These storms normally have such powerful updrafts that the top of the supercell storm cloud or anvil can break through the troposphere and reach into the lower levels of the stratosphere.
Supercell storms can be 24 kilometers or 15 miles wide.
In the United States,
A thunderstorm is classed as severe if winds reach at least 93 kilometers per hour or 58 miles per hour.
Hail is 25 mm or 1 inch in diameter or larger,
Or if funnel clouds or tornadoes are reported.
Severe thunderstorms can occur from any type of storm cell.
However,
Multicell,
Supercell,
And squall lines represent the most common forms of thunderstorms that produce severe weather.
A mesoscale convective system,
MCS,
Is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms,
But smaller than extratropical cyclones,
And normally persists for several hours or more.
A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape,
And include weather systems such as tropical cyclones,
Squall lines,
Lake effect snow events,
Polar lows,
And mesoscale convective complexes,
MCCs.
Most mesoscale convective systems develop overnight and continue their lifespan through the next day.
They tend to form when the surface temperature varies by more than 5°C or 9°F between day and night.
The type that forms during the warm season over land has been noted across North America,
Europe,
And Asia,
With a maximum in activity noted during the late afternoon and evening hours.
Forms of MCS that develop in the tropics are found in either the intertropical convergence zone or monsoon troughs,
Generally within the warm season between spring and fall.
More intense systems form over land than over water.
One exception is that of lake-effect snowbands,
Which form due to cold air moving across relatively warm bodies of water,
And occurs from fall through spring.
Polar lows are a second special class of MCS.
They form at high latitudes during the cold seasons.
The two major ways thunderstorms move are via advection of the wind and propagation along outflow boundaries towards sources of greater heat and moisture.
Many thunderstorms move with the mean wind speed through the Earth's troposphere,
The lowest 8 kilometers or 5 miles of the Earth's atmosphere.
Weaker thunderstorms are steered by winds closer to the Earth's surface than stronger thunderstorms,
As the weaker thunderstorms are not as tall.
Organized,
Long-lived thunderstorm cells and complexes move at a right angle to the direction of the vertical wind shear vector.
If the gust front or leading edge of the outflow boundary races ahead of a thunderstorm,
Its motion will accelerate in tandem.
This is more of a factor with thunderstorms with heavy precipitation than with thunderstorms with low precipitation.
When thunderstorms merge,
Which is most likely when numerous thunderstorms exist in proximity to each other,
The motion of the stronger thunderstorm normally dictates the future motion of the merged cell.
The stronger the mean wind,
The less likely other processes will be involved in storm motion.
On weather radar,
Storms are tracked by using a prominent feature and tracking it from scan to scan.
A back-building thunderstorm,
Commonly referred to as a training thunderstorm,
Is a thunderstorm in which new development takes place on the upwind side,
Usually the west or southwest side in the northern hemisphere,
Such that the storm seems to remain stationary or propagate in a backward direction.
Though the storm often appears stationary on radar,
Or even moving upward,
This is an illusion.
The storm is really a multi-cell storm with new,
More vigorous cells that form on the upwind side,
Replacing older cells that continue to drift downward.
While severe thunderstorms are most common in the spring and summer,
They can occur just about any time of the year.
Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards toward landscapes and populations.
One of the more significant hazards lightning can pose is the wildfires they are capable of igniting.
Under a regime of low-precipitation thunderstorms,
Where little precipitation is present,
Rainfall cannot prevent fires from starting when vegetation is dry,
As lightning produces a concentrated amount of extreme heat.
Any thunderstorm that produces hail that reaches the ground is known as a hailstorm.
Thunder clouds that are capable of producing hailstones are sometimes seen with green coloration.
Hail is more common along mountain ranges because mountains force horizontal winds upwards,
Known as orographic lifting,
Thereby intensifying the updrafts within thunderstorms and making hail more likely.
A tornado is a violent rotating column of air in contact with both the surface of the Earth and a cumulonimbus cloud,
Otherwise known as a thundercloud.
Or,
In rare cases,
The base of a cumulus cloud.
Tornadoes come in many sizes,
But are typically in the form of a visible condensation funnel,
Whose narrow end touches the earth and is often encircled by a cloud of debris and dust.
Most tornadoes have wind speeds between 40 and 110 miles per hour,
Or 64 and 177 kilometers per hour,
Are approximately 75 meters or 246 feet across,
And travel several kilometers,
A few miles before dissipating.
Some attain wind speeds of more than 300 miles per hour,
Or 480 kilometers per hour,
Stretch more than 1,
600 meters,
Or one mile across,
And stay on the ground for more than 100 kilometers,
Or dozens of miles.
Water spouts have similar characteristics as tornadoes,
Characterized by a spiraling funnel-shaped wind current that form over bodies of water,
Connecting to large cumulonimbus clouds.
Water spouts are generally classified as forms of tornadoes,
Or more specifically,
Non-supercelled tornadoes,
That develop over large bodies of water.
These spiraling columns of air frequently develop within tropical areas close to the equator,
But are less common within areas of high latitude.
Downburst winds can produce numerous hazards to landscapes experiencing thunderstorms.
Downburst winds are generally very powerful,
And are often mistaken for wind speeds produced by tornadoes,
Due to the concentrated amount of force exerted by their straight horizontal characteristics.
Downburst winds can be hazardous to unstable,
Incomplete,
Or weakly constructed infrastructures and buildings.
Agricultural crops and other plants in nearby environments can be uprooted and damaged.
Downburst winds are usually formed in areas when high-pressure air systems of downdrafts begin to sink and displace the air masses below it due to their higher density.
When these downdrafts reach the surface,
They spread out and turn into the destructive straight horizontal winds.
Most thunderstorms come and go fairly uneventfully.
However,
Any thunderstorm can become severe,
And all thunderstorms,
By definition,
Present the danger of lightning.
Thunderstorm preparedness and safety refers to taking steps before,
During,
And after a thunderstorm to minimize injury and damage.
Preparedness refers to precautions that should be taken before a thunderstorm.
Some preparedness takes the form of general readiness,
As a thunderstorm can occur at any time of the day or year.
Thunderstorms occur throughout the world,
Even in the polar regions,
With the greatest frequency in tropical rainforest areas,
Where they may occur nearly daily.
At any given time,
Approximately 2,
000 thunderstorms are occurring on Earth.
Kampala and Tororo in Uganda have each been mentioned as the most thunderous places on earth,
A claim also made for Singapore and Bogor on the Indonesian island of Java.
Other cities known for frequent storm activity include Darwin,
Caracas,
Manila,
And Mumbai.
Thunderstorms are associated with the various monsoon seasons around the globe,
And they populate the rain bands of tropical cyclones.
In temperate regions they are most frequent in spring and summer,
Although they can occur along or ahead of cold fronts at any time of year.
They may also occur within a cooler air mass following the passage of a cold front over a relatively warmer body of water.
Thunderstorms are rare in polar regions because of cold surface temperatures.
Some of the most powerful thunderstorms over the United States occur in the Midwest and the Southern states.
These storms can produce large hail and powerful tornadoes.
Thunderstorms are relatively uncommon along much of the west coast of the United States,
But they occur with greater frequency in the inland areas,
Particularly the Sacramento and San Joaquin Valleys of California.
In spring and summer,
They occur nearly daily in certain areas of the Rocky Mountains as part of the North American monsoon regime.
In the Northeast,
Storms take on similar characteristics and patterns as the Midwest,
But with less frequency and severity.
During the summer,
Air mass thunderstorms are an almost daily occurrence over central and southern parts of Florida.
