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Name: Jeff
Status: other
Grade: other
Location: CA
Country: N/A
Date: 4/1/2005

Why is the east coast and mid-west of the US prone to high humidity, and the west coast normally is not?


The part of the United States generally east of the Rocky Mountains receives moisture from the Gulf of Mexico, particularly during the warmer months of the year when the winds blow generally from the south. The water temperature is fairly high in the Gulf of Mexico, therefore the water evaporates more easily than Pacific Ocean water does (which has a lower temperature). Furthermore, a more westerly or northerly wind blows over the Pacific towards the west coast, bringing drier air from the northern Pacific or the Arctic.

One exception to the "drier west coast" idea is the Pacific Northwest, which during the cooler months of the year is usually humid, even rainy.

David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory

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