Strange Weather Phenomena • Severe Weather • Thunderstorms
Most thunderstorms flare up, throw some rain and lightning around, and collapse. Severe thunderstorms are what happen when moisture, instability, lift and wind shear organize convection well enough to start producing giant hail, destructive winds, tornadoes, flash floods and occasionally an entire evening that meteorologists would rather not have.
What makes a thunderstorm severe? This guide explains how dangerous thunderstorms form, how moisture and atmospheric instability fuel convection, why vertical wind shear organizes storms, how thunderstorms evolve into supercells, squall lines, bow echoes and mesoscale convective systems, and how those storms produce giant hail, damaging winds, tornadoes, flash flooding and intense lightning.
A thunderstorm becomes dangerous when its basic atmospheric ingredients combine strongly enough to support intense and persistent convection. Warm moist air supplies energy. Atmospheric instability allows rising air to accelerate. Lift initiates convection. Vertical wind shear determines whether the storm remains a short-lived cell or organizes into something far more durable — including a rotating supercell, a long squall line or a sprawling mesoscale convective system.
Severe Thunderstorms: Quick Facts
- Every thunderstorm produces lightning, but not every thunderstorm is severe.
- In the United States, severe-thunderstorm criteria generally include hail at least 1 inch in diameter and/or wind gusts of at least 58 mph.
- Tornadoes can develop from severe thunderstorms but are handled through dedicated tornado warnings.
- Heavy rain and lightning can be dangerous even when formal severe criteria are not met.
- The main ingredients for thunderstorms are moisture, instability and lift.
- Vertical wind shear strongly influences whether thunderstorms become organized and long-lived.
- Single-cell storms are usually short-lived.
- Multicell storms repeatedly regenerate new thunderstorm cells.
- Supercells contain persistent rotating updrafts and are among the most dangerous organized thunderstorms.
- Squall lines organize thunderstorms into long convective bands.
- Bow echoes are commonly associated with powerful straight-line winds.
- Mesoscale convective systems can persist for many hours and extend across hundreds of kilometers.
- Training thunderstorms can repeatedly cross the same area and cause extreme rainfall and flash flooding.
- Severe thunderstorms can produce several hazards simultaneously.
- A severe thunderstorm watch means conditions are favorable; a warning means severe weather is occurring or imminent.
What Is a Severe Thunderstorm?
A severe thunderstorm is a thunderstorm capable of producing damaging weather that exceeds defined meteorological thresholds.
Exact definitions vary between countries and forecasting agencies. In the United States, a thunderstorm is generally considered severe when it produces:
- hail at least 1 inch (2.54 cm) in diameter;
- wind gusts of at least 58 mph (50 knots / about 93 km/h);
- or tornado development, which triggers its own tornado-warning procedures.
A storm does not need to be officially classified as severe to be dangerous. Frequent lightning, torrential rain or localized flooding can threaten life even when hail and wind remain below formal warning thresholds.
Ordinary Thunderstorm vs Severe Thunderstorm
| Feature | Typical Thunderstorm | Severe / Organized Thunderstorm |
|---|---|---|
| Lightning | Yes | Yes |
| Heavy rain | Possible | Common |
| Updraft strength | Often modest or short-lived | Can be intense and persistent |
| Large hail | Usually absent | Possible to extreme |
| Damaging wind | Usually limited | Can be destructive |
| Tornado potential | Generally low | Higher in organized rotating storms |
| Organization | Often weak | May become highly organized |
| Longevity | Often short | Can persist for hours |
Ingredients for Severe Thunderstorms
Severe thunderstorms are not created by one magic atmospheric number. They develop when several ingredients overlap in the same place and at the same time.
The most important are:
- Moisture
- Atmospheric instability
- Lift
- Vertical wind shear
Moisture: Fuel for Deep Convection
Thunderstorms need water vapor, particularly in the lower atmosphere. Moisture may arrive from warm oceans, tropical air masses, monsoon circulations, moist boundary layers or large-scale transport from nearby seas.
As moist rising air cools and water vapor condenses, latent heat is released. That energy can increase buoyancy and strengthen the developing updraft.
Dew point is frequently used as a practical measure of low-level moisture. Higher dew points generally indicate more water vapor available to support deep convection.
Atmospheric Instability and CAPE
Atmospheric instability describes the tendency for displaced air to continue rising.
Strong instability commonly develops when warm, humid air near the surface lies beneath much colder air aloft.
Convective Available Potential Energy (CAPE) estimates the positive buoyant energy available to a rising air parcel.
Greater CAPE can support:
- stronger updrafts;
- deeper convection;
- larger hail potential;
- greater precipitation loading;
- stronger storm-scale vertical motions.
But CAPE alone does not produce severe thunderstorms. A highly unstable atmosphere can remain quiet if convection cannot begin or if storm organization is poor.
Convective Inhibition: The Atmospheric Cap
Convective inhibition (CIN) represents energy that suppresses free upward motion.
Too much inhibition can prevent thunderstorms from developing. A modest cap, however, can sometimes allow heat and moisture to accumulate before convection eventually breaks through, producing fewer but more intense storms.
Lift: What Starts the Storm?
Moist unstable air usually needs a mechanism that forces it upward.
Common triggers include:
- cold fronts;
- warm fronts;
- drylines;
- outflow boundaries;
- sea-breeze fronts;
- mountain slopes;
- surface convergence;
- upper-level disturbances;
- low-pressure troughs.
Vertical Wind Shear: The Organizer
Vertical wind shear is the change in wind speed and/or direction with altitude.
This is one of the most important ingredients separating ordinary short-lived thunderstorms from organized severe storms.
When shear is weak, rain and downdraft air often fall back through the storm’s updraft. The cool outflow spreads underneath the storm and quickly cuts off its supply of warm unstable air.
Stronger wind shear tilts the storm, helping separate:
- the updraft;
- heavy precipitation;
- downdrafts;
- cold outflow.
Directional shear can also supply rotation that strong updrafts may tilt vertically, helping storms develop organized rotating structures.
The Thunderstorm Life Cycle
A simple single-cell thunderstorm usually passes through three stages.
1. Developing or Cumulus Stage
Warm moist air rises rapidly and creates a growing cumulus tower. Upward motion dominates, while little precipitation reaches the ground.
2. Mature Stage
Rain and ice particles grow large enough to fall, producing downdrafts while the updraft remains active.
This is normally the storm’s most hazardous stage. Possible threats include:
- heavy rain;
- lightning;
- hail;
- strong wind;
- localized flooding;
- tornadoes in favorable environments.
3. Dissipating Stage
Downdrafts increasingly dominate the storm and cut off the supply of warm moist air. Rain weakens and the thunderstorm collapses.
How Thunderstorms Organize
Severe-weather potential depends not only on how strong an individual thunderstorm becomes, but also on how the convection organizes.
Storm mode is influenced by:
- instability;
- deep-layer wind shear;
- low-level wind shear;
- storm-relative inflow;
- cold-pool strength;
- surface boundaries;
- frontal orientation;
- large-scale atmospheric forcing.
Thunderstorms may organize as:
- single cells;
- multicell clusters;
- supercells;
- squall lines;
- bow echoes;
- quasi-linear convective systems;
- mesoscale convective systems.
Single-Cell and Multicell Thunderstorms
Single-Cell Thunderstorms
Single-cell thunderstorms are relatively short-lived storms dominated by one principal updraft and downdraft cycle.
They commonly form where wind shear is limited. Because precipitation eventually falls through the updraft, the storm often weakens within roughly an hour.
Pulse Severe Thunderstorms
Strong atmospheric instability can occasionally produce a rapidly intensifying single cell known as a pulse severe storm.
Pulse storms may briefly produce:
- large hail;
- strong convective winds;
- extreme rain;
- dangerous lightning.
Multicell Thunderstorms
Multicell storms contain multiple convective cells at different stages of development.
New updrafts repeatedly form along gust fronts, outflow boundaries or other convergence zones while older cells weaken.
Because the system continually replaces dying cells, a multicell cluster can survive for several hours and produce repeated hail, wind, heavy rain and lightning.
Supercells: The Most Organized Severe Thunderstorms
Among thunderstorm types, supercells are exceptionally organized and capable of producing some of the most extreme convective weather on Earth.
A supercell differs from an ordinary thunderstorm because it contains a persistent rotating updraft. Strong vertical wind shear helps separate the storm’s updraft from its precipitation and downdraft regions, allowing the storm to continue ingesting warm moist air for much longer than a typical thunderstorm cell.
Supercells can produce:
- giant hail;
- destructive winds;
- intense rainfall;
- frequent lightning;
- significant and sometimes violent tornadoes.
Radar may reveal organized rotation, while experienced observers may notice a persistent rotating updraft region and highly structured storm appearance.
Squall Lines
A squall line is a long, organized line of thunderstorms that can extend across a large region.
Squall lines commonly develop:
- along or ahead of cold fronts;
- near drylines;
- along strong convergence zones;
- within larger mesoscale convective systems.
The strongest convection frequently occurs along the leading edge, where advancing storm outflow lifts warm humid air.
Major hazards include:
- widespread damaging winds;
- frequent lightning;
- heavy rain;
- embedded tornadoes;
- localized large hail.
Bow Echoes
A bow echo is a curved radar structure that develops when part of an organized line of thunderstorms surges forward.
Bow echoes are strongly associated with destructive straight-line winds.
Rear-Inflow Jet
Strong winds may descend into the rear of the convective system and accelerate toward the bowing portion of the storm line.
When that momentum reaches the surface, severe winds can spread across a broad corridor.
Bookend Vortices
Rotating circulations may develop near the ends of a mature bow echo. These structures contribute to the organization and longevity of some convective wind systems.
Mesoscale Convective Systems
A Mesoscale Convective System (MCS) is a large organized thunderstorm complex operating on a scale larger than an individual storm but smaller than major synoptic weather systems.
MCSs can:
- survive for many hours;
- continue overnight;
- extend across hundreds of kilometers;
- produce hazards across several states, provinces or countries.
Common MCS Forms
- squall lines;
- bow echoes;
- quasi-linear convective systems;
- mesoscale convective complexes;
- large thunderstorm clusters.
Training Thunderstorms
In some systems, new thunderstorms repeatedly develop and move across the same location.
Meteorologists call this training because storm cells follow one another like train cars on the same track.
Training convection is one of the most important setups for extreme rainfall and flash flooding.
Recognizing a Dangerous Thunderstorm
Severe thunderstorms often look dramatic, but appearance alone cannot reliably determine which hazard a storm will produce.
Instead of treating cloud shapes as standalone severe-weather forecasts, look for the broader signs of an intensifying and organized storm:
- rapid vertical cloud growth;
- a persistent and powerful updraft;
- frequent or rapidly increasing lightning;
- large hail reports;
- strong inflow toward the storm;
- rapidly advancing outflow;
- radar-detected rotation;
- official severe-weather warnings.
Visual cloud identification belongs to the dedicated cloud and Sky Oddities guides. For specific storm-cloud structures, see:
For rotating storm anatomy, wall-cloud context, hook echoes and the internal structure of supercells, see
Supercell Structure Explained.
Major Severe-Thunderstorm Hazards
One severe thunderstorm can produce several hazards at the same time. This page explains why those hazards emerge from organized convection; each phenomenon has its own specialist guide for deeper science.
| Hazard | How the Thunderstorm Produces It | Full Guide |
|---|---|---|
| Tornadoes | Storm-scale rotation can become concentrated into a much smaller near-surface vortex. | Tornadoes Explained |
| Giant Hail | Powerful updrafts suspend growing ice particles within supercooled-water regions. | Giant Hail Explained |
| Damaging Winds | Downdrafts, convective outflow, momentum transfer, bow echoes and downbursts accelerate destructive winds toward the surface. | Extreme Wind Phenomena Explained |
| Flash Flooding | Extreme rainfall rates, slow movement and training convection overwhelm drainage and runoff systems. | Flash Floods Explained |
| Lightning | Collisions between ice particles, graupel and supercooled droplets create electrical charge separation inside the storm. | Lightning Explained |
Tornadoes
Tornadoes can develop when organized thunderstorm rotation becomes concentrated near the surface. Supercells are particularly important producers of significant tornadoes, although tornadoes can also form within linear convective systems.
Tornadogenesis depends on more than simply having a rotating storm. Low-level shear, inflow, boundaries, downdrafts and near-surface vorticity all interact on scales much smaller than the parent thunderstorm.
Giant Hail
Large hail requires an updraft strong enough to keep growing hailstones aloft while they collect supercooled liquid water and additional ice.
Organized thunderstorms — particularly supercells — provide some of the most favorable environments for exceptionally large hail.
Damaging Thunderstorm Winds
Severe thunderstorms can generate destructive winds without producing a tornado.
Important mechanisms include:
- strong downdrafts;
- microbursts and larger downbursts;
- gust fronts;
- bow echoes;
- rear-inflow jets;
- derechos;
- downward transport of high-momentum air.
These are wind phenomena, so their detailed formation, classification and damage patterns belong to
Extreme Wind Phenomena Explained.
Flash Flooding
Thunderstorms can produce enormous rainfall rates over small areas.
Flash-flood risk increases when storms:
- move slowly;
- repeatedly track across the same location;
- form within exceptionally moist air masses;
- develop over steep terrain;
- affect urban areas with extensive impermeable surfaces;
- occur where soil is already saturated.
Lightning
Every thunderstorm contains lightning because electrical charge becomes separated inside the convective cloud.
Strong organized storms may generate intense intracloud activity, frequent cloud-to-ground strikes, positive lightning and long-distance anvil discharges.
Lightning frequency can change rapidly as a storm intensifies, but lightning frequency alone does not determine whether a thunderstorm formally meets severe-warning criteria.
How Radar Detects Severe Thunderstorms
Weather radar is one of the most important tools for understanding a severe thunderstorm after convection has developed.
Radar does not simply show where rain is falling. Modern Doppler and dual-polarization radar can provide information about:
- precipitation intensity;
- storm motion;
- wind toward and away from the radar;
- rotation;
- hail;
- storm-scale structure;
- possible tornado debris;
- rainfall rates.
Reflectivity
Reflectivity indicates how strongly precipitation particles return radar energy.
Strong echoes can indicate:
- heavy rain;
- large concentrations of precipitation;
- hail within powerful convective cores.
Doppler Velocity
Doppler velocity measures the component of particle motion toward or away from the radar.
Adjacent strong inbound and outbound velocities may indicate organized rotation.
Correlation Coefficient
Dual-polarization radar helps distinguish different types of radar targets.
A localized area of unusually low correlation coefficient combined with strong rotation may indicate debris lofted by an ongoing tornado.
Hook Echo
A hook-shaped reflectivity signature can develop when precipitation wraps around a rotating supercell circulation.
Hook echoes are important indicators of organized rotation, but they do not automatically prove that a tornado is on the ground.
Three-Body Scatter Spike
Extremely large hail can create a radar artifact called a three-body scatter spike. It is an important clue that a storm may contain very large hail.
How Severe Thunderstorms Are Forecast
Severe-weather forecasting begins before a thunderstorm exists.
Meteorologists examine whether the atmosphere contains the ingredients necessary for strong convection and, critically, what type of storm organization those ingredients may support.
Key Forecast Parameters
- CAPE: buoyant energy available to rising air.
- CIN: inhibition suppressing convection.
- Dew point: low-level moisture.
- Lapse rates: temperature change with altitude.
- Deep-layer shear: important for organized storm mode.
- Low-level shear: important for near-surface rotation potential.
- Storm-relative helicity: measures streamwise rotational potential available to moving storms.
- Surface boundaries: fronts, drylines and outflow boundaries can focus storm initiation.
- Upper-level forcing: jet streaks, troughs and disturbances support ascent.
- Precipitable water: helps diagnose extreme-rainfall potential.
Weather Balloons
Radiosondes measure temperature, humidity, pressure, wind speed and wind direction through the atmosphere.
These vertical profiles allow meteorologists to calculate instability, estimate cloud-base conditions and assess wind shear.
Satellite Imagery
Satellites can reveal:
- rapidly growing cumulus clouds;
- cooling cloud tops;
- overshooting convection;
- moisture transport;
- frontal and boundary interactions;
- large-scale storm organization.
Radar
Once thunderstorms develop, radar becomes central to warning decisions because it can track:
- storm intensity;
- storm motion;
- rotation;
- hail cores;
- bowing line segments;
- possible tornado debris;
- rainfall intensity.
Storm Spotters and Ground Reports
Radar cannot directly observe everything occurring at ground level.
Reliable reports of hail size, wind damage, tornadoes and flooding remain extremely valuable for warning operations and post-storm verification.
Severe Thunderstorm Watch vs Warning
Watches and warnings describe different stages of risk.
| Alert | Meaning | Recommended Response |
|---|---|---|
| Severe Thunderstorm Watch | Atmospheric conditions are favorable for severe thunderstorms. | Monitor forecasts and be prepared to seek shelter. |
| Severe Thunderstorm Warning | Severe weather is occurring, indicated by radar, reported or imminent. | Move inside and away from windows. |
| Tornado Watch | Conditions favor tornado-producing thunderstorms. | Remain alert and know where you will shelter. |
| Tornado Warning | A tornado is occurring or strongly indicated. | Take tornado shelter immediately. |
| Flash Flood Warning | Flash flooding is occurring or imminent. | Move away from flood-prone areas and never drive into floodwater. |
Severe Thunderstorm Safety
Before Severe Weather Develops
- Check official weather forecasts and severe-weather outlooks.
- Know where you will shelter.
- Enable emergency alerts on your phone.
- Have more than one way to receive warnings.
- Charge phones and backup batteries.
- Secure loose outdoor objects.
- Move vehicles under sturdy cover if destructive hail is forecast.
During Damaging Wind or Hail
- Move inside a substantial building.
- Stay away from windows.
- Use an interior room when destructive wind is approaching.
- Do not shelter beneath trees.
- Do not go outside to protect vehicles once giant hail has begun.
During Tornado Conditions
- Move to a basement or interior room on the lowest floor.
- Stay away from windows.
- Protect your head and neck.
- Leave mobile homes for substantial shelter when sufficient warning exists.
During Lightning
- Move inside a substantial building or enclosed hard-topped vehicle.
- Avoid isolated trees.
- Leave beaches, open fields, water and exposed ridges.
- Do not assume you are safe simply because rain has not reached you.
During Flash Flooding
- Move toward higher ground.
- Never drive through flooded roads.
- Do not enter fast-moving floodwater.
- Avoid drainage channels, washes and low-lying crossings.
After the Storm
- Avoid downed power lines.
- Watch for unstable trees and branches.
- Stay away from flooded electrical equipment.
- Continue monitoring warnings because additional storms may follow.
Historic Severe Thunderstorm Outbreaks
The most useful historic severe-weather events are those that demonstrate how different forms of storm organization produce different hazards.
1974 Super Outbreak
The April 1974 Super Outbreak remains one of the defining examples of a widespread tornadic severe-weather environment. Numerous intense thunderstorms developed across a large region under powerful instability, lift and wind shear.
2011 Super Outbreak
The April 2011 outbreak demonstrated how a strongly sheared and unstable atmosphere can support numerous long-lived supercells and destructive tornadoes over a broad geographic area.
2020 Midwest Derecho
The August 2020 Midwest derecho illustrated a completely different severe-thunderstorm mode: a large, rapidly moving convective wind system producing widespread destructive straight-line winds rather than a classic supercell tornado outbreak.
Extreme Hail-Producing Supercells
Severe thunderstorms in North America, South America, Europe and Australia have produced hailstones large enough to damage roofs, vehicles, aircraft and agricultural systems.
Climate and Severe Thunderstorms
Severe thunderstorms depend on several atmospheric ingredients, and those ingredients do not necessarily change in the same direction.
Moisture
Warmer air can contain more water vapor, potentially increasing moisture availability and extreme rainfall where storm dynamics are favorable.
Instability
Changes in surface temperature and humidity can alter atmospheric instability and therefore the energy available to convective updrafts.
Wind Shear
Organized severe thunderstorms also depend strongly on vertical wind shear. Changes in shear may differ by region, altitude and season and do not necessarily mirror changes in surface temperature.
Storm Geography and Seasonality
Changes in moisture transport, storm tracks, frontal systems and seasonal temperature contrasts can affect where and when severe-thunderstorm environments develop.
Why Long-Term Trends Are Difficult to Measure
Observational records contain important complications:
- radar networks have improved;
- storm reporting has increased;
- population distribution has changed;
- hail and wind observations remain spatially incomplete;
- different countries use different severe-weather thresholds.
Severe Thunderstorm Myths and Misconceptions
| Myth | Reality |
|---|---|
| Every thunderstorm is severe. | All thunderstorms produce lightning, but only some meet formal severe criteria. |
| A huge amount of lightning automatically makes a storm severe. | Lightning is dangerous, but lightning frequency is not itself the standard U.S. severe-thunderstorm threshold. |
| Only supercells produce severe weather. | Multicells, squall lines and mesoscale convective systems can also produce destructive weather. |
| Every supercell produces a tornado. | Many supercells produce hail or damaging wind without becoming tornadic. |
| A hook echo proves there is a tornado. | A hook echo indicates organized storm structure; additional velocity, dual-polarization and surface evidence are needed. |
| Straight-line winds are harmless compared with tornadoes. | Convective winds can reach destructive speeds and produce extensive damage. |
| Flash floods require tropical cyclones. | Slow-moving and training thunderstorms can produce catastrophic flash flooding. |
| No rain overhead means lightning cannot reach you. | Lightning can strike far outside the main precipitation core. |
Legacy Article and Redirect Classification
Redirect a legacy article to this cornerstone when the dominant subject is the severe thunderstorm as an organized storm system rather than one specific hazard.
Redirect to Severe Thunderstorms Explained when the article is mainly about:
- a general severe-thunderstorm outbreak;
- a multicell severe-weather event;
- a squall line;
- a bow echo when the broader storm system is the focus;
- a mesoscale convective system;
- storm organization;
- storm evolution;
- multiple simultaneous hazards;
- severe convective forecasting;
- broad thunderstorm radar interpretation;
- a multi-hazard severe-weather event where no single hazard clearly dominates.
Redirect Elsewhere When a Specialist Topic Dominates
| Dominant Subject | Best Destination |
|---|---|
| Supercell anatomy, mesocyclones, LP/HP/Classic supercells, storm splitting, supercell radar structure | Supercell Structure Explained |
| Tornado formation, tornado outbreak, rating or tornado damage | Tornadoes Explained |
| Giant hail, hail records, hail damage or hail accumulation | Giant Hail Explained |
| Microbursts, downbursts, derechos, destructive straight-line winds or unusual wind phenomena | Extreme Wind Phenomena Explained |
| Flash flooding or extreme convective rainfall | Flash Floods Explained |
| Lightning strikes, records, fatalities, damage or lightning science | Lightning Explained |
| Shelf clouds or roll clouds | Shelf Clouds vs Roll Clouds Explained |
| Mammatus cloud appearance or formation | Mammatus Clouds Explained |
| Green storm skies as a visual phenomenon | Green Skies Explained |
Sources and Editorial Methodology
Severe-thunderstorm classification, radar interpretation, warnings and historic storm reports should be checked against official meteorological agencies and peer-reviewed atmospheric science whenever possible.
Preferred Primary Sources
-
NOAA National Weather Service
-
NOAA Storm Prediction Center
-
NOAA National Severe Storms Laboratory
- Environment and Climate Change Canada
- European Severe Storms Laboratory
- National meteorological agencies
- Official radar and storm-report databases
- Peer-reviewed convective-storm research
StrangeSounds Editorial Rules
- Distinguish severe-thunderstorm criteria from general thunderstorm hazards.
- Do not call every dramatic thunderstorm a supercell.
- Do not call every rotating cloud a tornado.
- Do not treat a hook echo as automatic proof of a tornado.
- Separate measured hail size from visual estimates.
- Separate sustained wind from wind gusts.
- Use radar, official warnings and credible storm reports together whenever possible.
- Do not treat lightning frequency as the sole measure of storm severity.
- Keep visual cloud identification within the Cloud / Sky Oddities cluster.
- Keep detailed supercell structure inside Supercell Structure Explained.
- Keep microbursts and downbursts within the Extreme Wind Phenomena cluster.
- Redirect legacy articles according to the dominant phenomenon, not merely the most dramatic word in the headline.
Frequently Asked Questions About Severe Thunderstorms
What is a severe thunderstorm?
A severe thunderstorm is a thunderstorm producing sufficiently large hail, damaging winds or other severe convective hazards according to criteria established by the relevant meteorological agency.
What counts as a severe thunderstorm in the United States?
The National Weather Service generally uses hail at least 1 inch in diameter and/or wind gusts of at least 58 mph as severe-thunderstorm criteria.
What are the main ingredients for severe thunderstorms?
Thunderstorms require moisture, atmospheric instability and lift. Vertical wind shear becomes especially important when determining whether convection can organize into long-lived severe storms.
What is CAPE?
CAPE, or Convective Available Potential Energy, estimates the positive buoyant energy available to a rising parcel of air.
What is vertical wind shear?
Vertical wind shear is the change in wind speed and/or direction with altitude. It strongly influences thunderstorm organization, storm motion and longevity.
What makes supercells different from ordinary thunderstorms?
Supercells contain persistent rotating updrafts and can remain organized much longer than ordinary thunderstorm cells. Complete supercell anatomy is covered in the dedicated Supercell Structure Explained guide.
Do all supercells produce tornadoes?
No. Many supercells produce giant hail or damaging winds without producing tornadoes.
What is a squall line?
A squall line is an organized line of thunderstorms capable of producing widespread damaging winds, heavy rain, lightning and embedded tornadoes.
What is a bow echo?
A bow echo is a curved radar structure that develops when part of a convective line accelerates forward. Bow echoes are commonly associated with damaging straight-line winds.
What is a mesoscale convective system?
A mesoscale convective system is a large organized thunderstorm complex capable of persisting for many hours and extending across hundreds of kilometers.
What are training thunderstorms?
Training occurs when successive thunderstorms repeatedly move across the same location, greatly increasing extreme-rainfall and flash-flood risk.
Does frequent lightning mean a thunderstorm is severe?
Not necessarily. Lightning can be extremely dangerous even when the storm does not meet formal severe hail or wind criteria.
Can severe thunderstorms produce destructive winds without tornadoes?
Yes. Bow echoes, strong downdrafts, microbursts, downbursts and other convective wind mechanisms can produce destructive straight-line winds without a tornado.
Where do microbursts and downbursts belong?
They are thunderstorm-generated wind phenomena, so their detailed formation, classification and damage patterns are covered under Extreme Wind Phenomena Explained.
Can thunderstorms cause flash floods without being formally severe?
Yes. Torrential rainfall can produce deadly flash flooding even when hail and wind remain below official severe-thunderstorm thresholds.
What is the difference between a severe thunderstorm watch and warning?
A watch means atmospheric conditions are favorable for severe thunderstorms. A warning means severe weather is occurring, has been reported, is indicated by radar or is imminent.
Can a severe thunderstorm warning be issued without a watch?
Yes. Severe thunderstorms can occasionally develop quickly enough that a warning is issued even when no watch is already in effect.
What should you do during a severe thunderstorm warning?
Move inside a sturdy building, stay away from windows and continue monitoring official alerts for tornado, flash-flood or additional severe-weather warnings.
Where should old supercell articles redirect?
Articles primarily about supercell anatomy, mesocyclones, rotating updrafts, LP/Classic/HP supercells, hook echoes or detailed supercell radar structure should redirect to Supercell Structure Explained. Broader multi-hazard thunderstorm articles can redirect here.
Where should old giant-hail articles redirect?
Redirect them to Giant Hail Explained when hailstone size, hail records, hail accumulation or hail damage is the dominant subject.
Where should old tornado articles redirect?
Redirect them to Tornadoes Explained when tornado formation, tornado damage, tornado ratings or tornado outbreaks are the main subject.
Where should old lightning articles redirect?
Redirect them to Lightning Explained when lightning science, records, strikes, fatalities or lightning damage dominate the article.
Where should severe-wind articles redirect?
Articles mainly about downbursts, microbursts, derechos, straight-line winds or other destructive wind mechanisms should redirect to Extreme Wind Phenomena Explained.
Where should flash-flood thunderstorm articles redirect?
Redirect them to Flash Floods Explained when extreme rainfall and rapid flooding dominate the story.
