Bodega Bay weather station will measure streams of wet air

A new weather observation station will be constructed at Bodega Bay to monitor low-lying streams of moisture-laden air that sweep ashore and account for half of the rain that falls in coastal California.

They are in scientific terms "atmospheric rivers," and are a well-known but little understood concept.

"Think of a river on the ground, it is a channel where the water is flowing ... this is a channel in the sky where intense water vapor is flowing," said Allen White, a researcher with the National Oceanic and Atmospheric Administration in Boulder, Colo.

The atmospheric river that typically comes to mind is the so-called Pineapple Express, which forms near Hawaii and is a veritable freeway for wet storms that can soak the coast and in some years cause the Russian River to flood.

"The really dangerous thing is when the cold front stalls, and the river stays in place for a long time," White said. "That happened this year in Southern California. The river stalled and you had 28 inches of rain in three days."

These rivers of cold air come in from the west, dropping moisture as they rise up over the coastal mountains, the reason that Cazadero gets three times more rain than Bodega Bay, White said.

The first research data on the phenomenon has been provided by an unmanned weather station operated for a dozen years by NOAA at UC Davis' Bodega Marine Lab, gathering wind speed, temperature, moisture and atmospheric pressure.

It will be replaced by a newer and more efficient station at the lab, with an enhanced ability to see rain and wind that even weather satellites can't identify.

Other stations will be built at Eureka, Point Sur and Santa Barbara, creating a picket fence of observatories along the California coast, White said.

The new stations have radar that is more sophisticated to measure what's happening in the first few miles of the earth's atmosphere, where these atmospheric rivers are found.

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