Rain and wind on way for holiday

Cloudy skies and cool temperatures today will give way to a wet, windy Christmas Day in the Bay Area, marking the second bout of measurable rainfall within the past two weeks.

A storm system is set to arrive in the North Bay starting early Friday morning, lowering temperatures to the mid- to high 50s and spreading rain throughout the region as it moves eastward, according to the National Weather Service.

Rainfall totals will be highest in Sonoma County. Coastal mountains and areas scorched by the 2020

Meyers and Wallbridge wildfires could see up to 2.5 inches, interior mountains up to 1.5 inches and valleys up to 1.25 inches.

The weather service is monitoring conditions closely out of concern that heavy rain could cause debris flow along burn scars, said meteorologist David King.

“We don't have a watch out for any flash flooding right now, but if the system ends up producing big rain rates, we could,” King said.

The forecast for the rest of the Bay Area calls for 0.25 inch to an inch of rain, a welcome boost to low rainfall totals since the season began on Oct. 1.

A brief bout of showers in mid-December brought some reprieve — upping San Francisco's rainfall totals to about 28% of normal as compared with just 9% — but the region is still way off track, King said.

San Jose has hit just 20% of its normal rainfall, and Oakland is at 23% and Santa Rosa 29%. Watsonville, which has seen the most rain across the region, still hovers at just 46% of normal.

“We're looking forward to having another system to help us out,” King said.

Southerly winds are expected to accompany the system, with speeds ranging from 20 to 30 mph in the North Bay mountains and East Bay hills; 15-25 mph in the Santa Cruz Mountains, South Bay hills and on the coastside of the Peninsula; 10-20 mph in the North Bay and East Bay valleys; 10-15 mph on the bayside of the Peninsula; and 5-15 mph in the South Bay valleys.

The winds could knock down loose branches and diseased or weak trees, the weather service warned.

Skies likely will clear Saturday morning, but another round of rain could arrive as soon as Sunday.

Although the system is still too far out to predict with certainty, the weather service said rainfall totals could range from .5 inch in the North Bay to 2.5 inches in Big Sur.