It forms above the gust front as warm air ahead of the storm rides over the cool outflow from the thunderstorm. Shelf cloud - a low-level, wedge-shaped cloud attached to the thunderstorm. Severe thunderstorm - A thunderstorm producing damaging winds (trees down, etc.) or winds 58 mph or more and/or hail three-quarter of an inch or greater in diameter. By the untrained, these can be misinterpreted as tornadoes, since they can hang low to the ground. These clouds are ragged and wind torn and are not usually attached to the thunderstorm. Scud clouds - Low cloud fragments often seen in association with and behind thunderstorm gust fronts. It is detached from the thunderstorm on its leading edge.

The cloud takes on the shape of a horizontal tube that appears to be rolling. The motions of the warm air riding up and over the cool air moving down and under creates a swirling of air or an eddy. Roll cloud - on rare occasions, a shelf cloud may turn into a roll cloud. This marks the updraft of a thunderstorm. Rain-free base - the dark underside of a cloud (its base) that has no visible precipitation falling from it. Precipitation shaft - a visible column of rain or hail falling from the base of the cloud. Microburst - A small downburst affecting an area less than 2.5 km in diameter.

With thunderstorms, they are usually seen under the anvil and often accompany severe thunderstorms. Mammatus (or mamma clouds) - these clouds appear to be hanging, rounded protuberances or pouches on the underside of the cloud. Macroburst - A larger downburst affecting an area greater than 2.5 km in diameter. This signature is in the radar reflectivity field Doppler radar's velocity information can help confirm the presence of a tornado, especially when a hook echo exists in the reflectivity field. The updraft is the hollow portion of the hook (looks like a backwards 'J' or a 6) and is where the tornado would most likely be found (if the storm were to produce one). The rain echo forms the hook pattern as air rotates around the strong updraft. Hook echo - A radar pattern sometimes observed in the southwest (right, rear) quadrant of a tornadic thunderstorm. Hail - Precipitation in the form of balls or clumps of ice. It is usually felt as a change to gusty cool winds and often precedes the thunderstorm's rain by several minutes. Gust front - the leading edge of the thunderstorm's downdraft of air as it spreads out away from the storm. It is associated with a rotating column of air that has condensed to form a cloud. It is most frequently associated with strong or severe thunderstorms.įunnel cloud - a funnel-shaped cloud extending from a towering cumulus or thunderstorm.

The cloud line has roughly a stair-step appearance with the taller clouds adjacent to the parent cumulonimbus. It is most often accompanied by rain.įlanking line - A line of cumulus clouds connected to and extending outward from the most active portion of a parent cumulonimbus, usually found on the southwest (right, rear) side of a storm. Viewing the damage from the air does not reveal evidence of a twisting motion or convergence toward a central track, like it would for a tornado.ĭowndraft - A column of cool air that sinks toward the ground. It usually occurs near the leading edge of the storm or may occur in heavy rain. As the cloud and cloud droplets grow in size, the base will begin to gray.ĭownburst - A sudden rush of cool air toward ground that can impact with speeds greater than 70 mph and produce damage similar to that of a tornado. Tufts are rising columns of air condensing. With long-lasting thunderstorms, the anvil may spread more than 100 miles downwind.Ĭumulus cloud - a cauliflower-shaped cloud with a flat base and sharp edges.

It usually has a fibrous or smooth appearance. Anvil - The spreading out (by strong winds) of the upper portion of the thunderstorm.

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