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Storm chasing glossary
The words chasers and forecasters use, in plain English.
- Anvil
- The flat, spreading top of a thunderstorm where the updraft hits the top of the troposphere and fans out.
- Bounded weak echo region (BWER)
- A hole in the radar echo where a strong updraft is carrying precipitation upward faster than it can form — a sign of a very strong updraft.
- Bow echo
- A bow-shaped line of storms on radar, often producing damaging straight-line winds.
- Cap
- A layer of warm air above the surface that suppresses storms until something breaks it. A strong cap can delay storms and make them more explosive when they form.
- CAPE
- Convective available potential energy — a measure of how unstable the air is and how strong an updraft could become.
- Clear slot
- A gap of clearer sky wrapping around a mesocyclone, associated with the rear-flank downdraft.
- Cone tornado
- A tornado that is narrower at the ground than at the cloud base.
- Core punching
- Driving through the heavy rain and hail core of a storm to reach the other side. Dangerous and discouraged.
- Debris ball
- A concentrated radar signature of debris lofted by a tornado, indicating a damaging tornado on the ground.
- Doppler radar
- Radar that measures the motion of precipitation toward or away from it, as well as how much there is.
- Dryline
- A boundary between moist air and dry air, common on the Plains, where storms often develop.
- EF scale
- The Enhanced Fujita scale, which rates tornadoes from EF0 to EF5 by the damage they cause.
- Forward-flank downdraft (FFD)
- The region of heavy rain and hail on the leading side of a supercell.
- Funnel cloud
- A rotating cone of condensed cloud that does not reach the ground. When it touches the ground it is a tornado.
- Gust front
- The leading edge of cool air flowing out of a thunderstorm, often marked by a shelf cloud.
- Hail core
- The area of a storm with the largest hail, shown in red or magenta on radar reflectivity.
- Hook echo
- A hook-shaped extension on the radar echo of a supercell, often near a tornado.
- Inflow
- Warm, moist air drawn into a storm to feed its updraft.
- Inflow band
- A line of low clouds feeding into the updraft of a storm.
- Landspout
- A weak tornado that forms from the ground up, usually not associated with a rotating supercell.
- Mammatus
- Pouch-like clouds that hang below an anvil. They are not a sign of a tornado.
- Mesocyclone
- The rotating updraft inside a supercell, a few miles wide.
- Multiple-vortex tornado
- A tornado containing several smaller whirls circling a common centre.
- Outflow boundary
- A boundary of cool air created by a thunderstorm’s downdraft.
- Rear-flank downdraft (RFD)
- A descending stream of air on the back side of a supercell that can help tighten rotation at the ground.
- Reflectivity
- How strongly precipitation reflects the radar beam; the usual colour radar map, measured in dBZ.
- Rope tornado
- A thin, twisting tornado, often in its dissipating stage.
- Shelf cloud
- A low, wedge-shaped cloud along the gust front of a storm line.
- SKYWARN
- The National Weather Service’s volunteer spotter program, with free training.
- Spotter
- A trained volunteer who reports severe weather to the weather service.
- Stovepipe tornado
- A narrow tornado with an almost constant width from cloud to ground.
- Supercell
- A thunderstorm with a persistent rotating updraft, responsible for most strong tornadoes.
- Tornado warning
- An alert that a tornado is occurring or imminent, based on a sighting or on radar. Take shelter immediately.
- Tornado watch
- An alert that conditions are favourable for tornadoes in an area. Stay aware and have a plan.
- Updraft
- The column of rising air that powers a storm.
- Velocity couplet
- Adjacent areas of strong inbound and outbound winds on Doppler velocity, indicating rotation.
- Wall cloud
- A lowered, often rotating cloud base beneath a supercell’s updraft where tornadoes often form.
- Waterspout
- A rotating column of air over water; some are tornadoes that moved offshore, most form in fair weather over warm water.
- Wedge tornado
- A tornado that is wider than it is tall, appearing as a dark wall under the storm.
- Wind shear
- A change in wind speed or direction with height. Strong shear is a key ingredient for supercells.
Last reviewed 2 November 2026