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How are isobars used by meteorologists?

Isobars are lines of constant or equal pressure on a weather map. They can be used to find areas of low or high pressure over a broad area (like the U.S.), and they can tell us how intense the system may be.

Explanation:

the answer is: they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur twice a year in the spring and fall.