SAN FRANCISCO (AP) — A late-season atmospheric river over the Pacific is taking aim at northern and central California.
The National Weather Service says the “robust” plume of subtropical moisture is well offshore Wednesday but stretches all the way to Hawaii.
Forecasters say it’s not clear where it will make landfall, but light rain is expected to develop in the North Bay by Thursday
afternoon. Rainfall is then expected to spread south across the rest of the San Francisco Bay Area and into the Monterey Bay Area
late Thursday and Thursday night. Rainfall intensity through Thursday night is expected to be light to moderate.
Rainfall intensity is forecast to increase on Friday and rain rates could be heavy at times by Friday afternoon, according to the National Weather Service. Periods of heavy rain are then possible through Friday night and into early Saturday morning.
Rainfall is expected to taper off by midday Saturday.
Rainfall totals from late Thursday through midday Saturday are forecast to range from 2 to 4 inches across the North Bay except in the North Bay Mountains where totals are projected to be closer to 4 to 6 inches. Rainfall totals forecast for the Santa Cruz Mountains are also in the 4 to 6 inch range.
Local amounts of more than 6 inches are possible in the wettest locations of the North Bay Mountains and Santa Cruz Mountains.
Current rainfall projections indicate the Russian River and Napa River will see significant rises late this week and into the weekend, but remain well within their banks. There is a chance some smaller rivers and streams in the North Bay could flood, especially if heavy rain rates persist across a watershed longer than anticipated.
The heavy rain across the North Bay burn scars could trigger flash flooding or mudslide/debris flows across and downstream from the burn scars. Outside of the burn scars, widespread landslides are not expected from this event
The potential for flooding will also be a concern in the Central Valley and in parts of the Sierra Nevada, where storm runoff could combine with melting snow at lower elevations. Snowfall will be limited to high elevations because of the storm’s warmth.
Southern California will be out of the picture, except for light rain over San Luis Obispo and Santa Barbara counties.
© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.