Meteorological Terms

ANVIL
The top portion of a mature thunderstorm that has the appearance of having been “blown off.”

ARC CLOUD
Also sometimes called a shelf cloud. This is usually the dark, ominous looking cloud formation the precedes the passage of a squall line or multi-cell thunderstorm formation. It is formed as warm moist air overrides cool downdraft winds at the leading edge of the thunderstorm (the gust front).

CELL
The basic thunderstorm, which consists of one updraft and one downdraft.

DEBRIS CLOUD
Area of dust, sand, and debris that forms near the ground at the base of a tornado.

DOWNBURST
A small area of rapidly descending air beneath a thunderstorm. Downburst winds hit the ground and spread out, often at speeds in excess of 100 mph. See also downdraft, macroburst and microburst.

DOWNDRAFT
Area within a thunderstorm where the predominant air motion is downward. Where there is precipitation there will always be a downdraft. Downbursts are localized areas within the downdraft of very rapidly descending air.

FUNNEL (CLOUD)
Generally the funnel is a visible tornado that hasn’t yet reached the ground. Funnels consist of water droplets that have condensed due to the rapid temperature and pressure changes in the vicinity. Also called condensation funnel.

GUST FRONT
The area near the leading edge of a thunderstorm where downdraft winds hit the earth’s surface and spread out. The gust front is the leading edge of the spreading winds. The gust front is usually found just below or very near the arc cloud.

HAIL
Large ice chunks that grow within the thunderstorm until they are too heavy to be supported by the mechanics within the storm. Large hailstones fall at speeds greater than 100 mph.

INFLOW
Area of a thunderstorm where air from the surrounding environment is “sucked up” into the thunderstorm updraft. The inflow area is always void of precipitation and the cloud bases are dark and flat.

MACROBURST
A downburst with a diameter of greater than 2.5 miles.

MAMMATUS
Downward protruding “bumps” usually on the underside of the anvil of a thunderstorm. Mammatus (“Mama”) clouds are indicative of extreme turbulence.

MICROBURST
A downburst with a diameter of 2.5 miles or less.

OUTFLOW
That portion of the thunderstorm where the downdraft winds hit the surface of the earth and spread out.

OVERSHOOTING TOP
A protruding cloud area above the usually smooth anvil of a mature thunderstorm that indicates the presence of an intense updraft.

SCUD (CLOUD)
Clouds that appear to have broken off beneath the base of a thunderstorm. Scud (fractus) clouds often may reach to near the ground and can be easily mistaken for a funnel.

SHELF CLOUD
See Arc Cloud

TAIL CLOUD
Scud-type cloud that forms near the base of a wall cloud and protrudes almost parallel to the earth toward the main precipitation shaft of the thunderstorm.

TORNADO
Rotating area of strong winds and rapid pressure change that sometimes forms in conjunction with a severe thunderstorm.

UPDRAFT
The area within the thunderstorm where the predominant air motion is upward.

VAULT
An area of dry clear air that often forms between the main precipitation shaft and the rain-free base wall cloud.

WALL CLOUD
A rotating cloud that forms beneath the base of the thunderstorm behind the main precipitation shaft where some of the inflowing air and outflowing air meet and mix. Tornadoes, if they occur, will appear to drop out of the wall cloud.