First of two atmospheric rivers enters California. Officials advise storm prep(Part-2)

The biggest impact will be runoff from significant rainfall that will probably flood several streams, said Robert Hart, a western National Weather Service meteorologist.

The meteorological service issued a flood watch for the Bay Area and Central Coast until Friday AM due to probable flooding of rivers, streams, highways, and wildfire-scarred regions. On Thursday and Friday, forecasters predicted 18-foot (5.4-meter) waves on the Central Coast.

Last winter, drought-busting atmospheric rivers caused widespread floods, large waves that pounded coastline villages, and record-breaking snowfall that destroyed houses in California. More than 20 perished.

Joshua Whitby, kitchen manager of Zelda's on the Beach in Capitola, Monterey Bay, brought sandbags and pondered boarding up the restaurant. The second storm in the sequence might be stronger, according to UC Los Angeles climate expert Daniel Swain.

In an online briefing Tuesday, Swain said models show bombogenesis, a spinning low-pressure system quickly deepening, might increase as it reaches California. The procedure is dubbed a “cyclone bomb.”

Swain said that scenario may bring a severe windstorm to the San Francisco Bay Area and Northern California, as well as significant but short rain.

Swain said a deep tap of Pacific moisture extending to the tropics will bring southern California less wind but two to three times as much rain as the north. New storms halfway through a winter are different from last year.

Despite storms like a Jan. 22 rain that caused flash floods in San Diego, the trend has been dryer. State authorities said Tuesday that the Sierra Nevada snowpack, which supplies 30% of California's water, is half its average.