“Short waves” on weather maps

Weather Blog
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Dear Tom,
Sometimes you show a “shortwave” on a weather map, depicted as a dashed black line. What is it?

Steve Hanan, Morton Grove

Dear Steve,
A shortwave, also known as a shortwave trough, is a mid or upper-atmospheric disturbance that induces upward motion ahead of it. If other conditions are favorable, the upward motion contributes to the development of clouds and precipitation ahead of it. Shortwaves are embedded in the longwave atmospheric flow pattern that circles the Earth steering the storms and air masses that determine this planet’s weather. Meteorologists, aided by computer models, track the movement of the short waves to help forecast the onset and duration of precipitation events. Shortwaves are visible as cloudy areas on satellite loops.


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