Mesocyclone
A rotating vortex of air within a supercell thunderstorm, typically 2-6 miles in diameter. Mesocyclones are detected by Doppler radar and indicate the potential for tornado development.
More Severe Weather Terms
Tornado
A tornado is a violently rotating column of air in contact with the ground, extending from a thunderstorm. Tornadoes are rated from EF0 to EF5 on the Enhanced Fujita scale by the damage they cause. Most last less than 10 minutes, but the strongest can stay on the ground for more than an hour.
Supercell
A supercell is a thunderstorm with a deep, persistently rotating updraft called a mesocyclone. Supercells are the most dangerous type of thunderstorm: they produce nearly all significant tornadoes in the United States and most hail larger than golf balls, along with damaging winds and flash flooding.
Derecho
A derecho is a widespread, long-lived windstorm produced by a fast-moving line or cluster of severe thunderstorms. Under the criteria the Storm Prediction Center uses, the swath of wind damage must be at least 250 miles (about 400 km) long, with gusts of at least 58 mph along its length and several well-separated gusts of 75 mph or greater.
Microburst
A localized column of sinking air that produces damaging divergent winds at or near the surface. Microbursts can produce winds exceeding 100 mph in an area less than 2.5 miles across and are particularly hazardous to aircraft.
Downburst
A strong downdraft that induces an outward burst of damaging winds at or near the surface. Downbursts can be either microbursts (less than 2.5 miles) or macrobursts (larger than 2.5 miles) and can cause damage similar to a tornado.
Wall Cloud
An isolated lowering of a rain-free cloud base, typically found on the south or southwest side of a supercell. Wall clouds often rotate and may produce a funnel cloud or tornado. They usually precede tornado formation by 10-20 minutes.
Funnel Cloud
A rotating cone-shaped cloud extending downward from the base of a thunderstorm but not reaching the ground. When a funnel cloud touches the ground, it becomes a tornado.
Enhanced Fujita Scale
The Enhanced Fujita (EF) scale rates tornadoes from EF0 to EF5 based on the damage they cause. Surveyors compare the damage to 28 kinds of buildings, structures, and trees against expected levels of damage, then estimate the 3-second wind gust responsible. EF0 means estimated gusts of 65 to 85 mph, and EF5 means over 200 mph.
Flash Flood
A flash flood is a rapid and extreme flow of high water into a normally dry area, or a rapid rise in a stream or creek above flood level, that begins within about six hours of its cause. The usual cause is intense rainfall, but a dam failure or an ice jam can also trigger one.
Squall Line
A squall line is a line of active thunderstorms, either continuous or with breaks, together with the rain areas the storms produce. Squall lines can extend for hundreds of miles and last for many hours. Their main hazard is straight-line wind damage, though tornadoes sometimes form along the leading edge.
Shelf Cloud
A shelf cloud is a low, horizontal, wedge-shaped cloud attached to the base of a thunderstorm along its gust front, the leading edge of the storm's rain-cooled outflow. Rising cloud motion is often visible on its leading edge, while the underside looks turbulent and wind-torn. It means gusty winds are about to arrive.
Mesocyclone: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
Weather Education
How Tornadoes Form: Types, EF Scale, and Safety
Learn how tornadoes form from supercell thunderstorms, the Enhanced Fujita scale, types of tornadoes, and critical safety steps to protect yourself.
Guides
How to Read Satellite Imagery: A Complete Guide to Weather From Space
Master visible, infrared, and water vapor satellite imagery. Learn the science behind each channel and how meteorologists use them to track storms.
Guides
Weather Radar Colors Explained: How to Read Radar Like a Pro
Learn what weather radar colors mean, from light green to purple. Understand reflectivity, precipitation intensity, and how to interpret radar images.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Seasonal Hub
Tornado Season Guide
Peak tornado timing by region, safety planning, and how warnings work.
Use Case
WeatherAI for Storm Chasers
See how WeatherAI supports active storm tracking with radar, severe weather context, and storm-focused workflows.
Feature
Severe Weather
Follow outlooks, watches, warnings, and storm signals in one severe-weather workflow.
Glossary
Doppler Radar
Doppler radar is weather radar that measures the motion of precipitation as well as its location and intensity.
Explore Other Terms
Hail
Balls or irregular lumps of ice produced in severe thunderstorms. Hailstones form when updrafts carry raindrops into extremely cold areas of the atmosphere where they freeze. Repeated cycles through the updraft can create hailstones larger than softballs.
Barometric Pressure
The weight of the atmosphere pressing down on a given point, measured in inches of mercury (inHg) or millibars (mb). Rising pressure typically indicates improving weather, while falling pressure suggests approaching storms or precipitation.
Reflectivity
A measure of how much radar energy is reflected back by precipitation, measured in dBZ (decibels of Z). Higher values indicate heavier precipitation or larger particles. Values above 50 dBZ typically indicate heavy rain or hail.
CAPE
CAPE (Convective Available Potential Energy) is the amount of energy a rising parcel of air can draw from the atmosphere, measured in joules per kilogram (J/kg). The higher the CAPE, the faster a storm's updraft can rise, and the stronger thunderstorms can become once something sets them off.
IFR
Instrument Flight Rules govern flights conducted under instrument procedures and can be used in clear weather too. Separately, the IFR weather category means a ceiling from 500 to less than 1,000 feet and/or visibility from 1 to less than 3 statute miles, with lower values classified as LIFR. Legal operating requirements depend on airspace, regulations, equipment, and pilot qualifications.
Invest
A weather system designated for investigation by the National Hurricane Center. An Invest designation triggers enhanced data collection and model runs but does not indicate expected development. Many Invests never become tropical cyclones.
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