What is the difference between “isolated” and “scattered” thunderstorms or rain showers?

Dear Tom,

What is the difference between “isolated” and “scattered” thunderstorms or rain showers?

Marc Rubin,
Highland Park

Dear Marc,
The terms “isolated” and “scattered” refer to the areal coverage of the precipitation event. “Scattered” is used to reference showers or thunderstorms that are occurring across 1/8 through 4/8 of the total area covered by a particular weather forecast or radar image. “Isolated” refers to showers or thunderstorms whose areal coverage is less than 1/8 of this area. Another term, “likely”, refers to showers or thunderstorms whose areal coverage ranges from 5/8 through 6/8 of the total area under consideration. Precipitation mentioned without a coverage qualifier refers to precipitation that is occurring across 7/8 or more of the area. These terms are also used to refer to the amount of the sky covered by clouds.

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