Flood Watch In Effect As Atmospheric River Slams Bay Area Wednesday

SAN FRANCISCO — A powerful atmospheric river will slam into the Bay Area on Wednesday, promising heavy rain, strong winds and potential flood hazards over the next few days, according to the latest forecasts.

The National Weather Service encouraged residents Tuesday to take advantage of the calm before the storm and prepare for what is ahead.

"Perfect time to clear out the gutters, tie down the outdoor furniture and trash cans, check the batteries in the weather radio, and make sure your go-bag is nicely stocked," the weather service said. "Today will be the last day of our pleasant stretch of weather."

According to the San Francisco Chronicle, the incoming storm could prove to be the season's strongest so far, and the blast of moisture will fuel heavy snow in the mountains, where major impacts are expected into Thursday.

A flood watch will take effect across the Bay Area and Central Coast at 4 a.m. Wednesday and remain in place until at least Friday morning. Rivers in the North Bay, which is likely to see some of the heaviest rain, will be the most at risk for flooding.

"The likelihood of reaching flood stage at mainstem rivers across the North Bay has increased to a 30 - 50 percent chance at the Russian River at Guerneville, the Napa River at Saint Helena, and the Napa River at Napa," forecasters said Tuesday. "A 15 - 35 percent chance of reaching flood stage remains for the Russian River at Healdsburg in the North Bay and the San Lorenzo River at Big Trees in Santa Cruz County."

Moderate to heavy rain is likely regionwide Wednesday, and even rain-shadowed areas are favored to see at least an inch of precipitation. San Francisco, the Peninsula, and southern portions of the North Bay could pick up 2 to 3 inches of rain, with 1 to 2 inches in the forecast for the Santa Clara Valley, interior East Bay and San Benito County. Northern and coastal areas of the North Bay may see 4 to 6 inches of rain.

New forecasts show the highest rain rates beginning in the afternoon for the North Bay before the band spreads south and east throughout the evening. Thursday's rain should be lighter, with lingering showers, but a few stormy pockets may emerge.

Forecasters warn strong gusts will present another hazard with the storm, and the National Weather Service has issued wind advisories and warnings to take effect across the Bay Area early Wednesday. Most areas may see gusts of 40 mph or higher, enflaming risks for downed trees and power outages.

"The Wind Advisory has been expanded across the [warning area] with a High Wind Warning issued for the Santa Cruz and Santa Lucia mountain ranges," the weather service said. "Wednesday is looking as much of a wind event as it is a rain event."

The weather should transition to a more showery pattern Friday and Saturday, but forecasters are also keeping an eye on an atmospheric river waiting in the wings that could kick up more heavy rain and wind by late in the weekend.