As dry December ends, rain possible in early January

As the Bay Area prepares to bid farewell to 2017 and one of the driest Decembers on record, the new year could also bring the first rain to the region in more than two weeks.

Although the timing remains uncertain, the National Weather Service said computer models are in agreement that much of California could receive rainfall in the middle of next week.

“We’re cautiously optimistic with this forecast,” said Scott Rowe, a meteorologist with the weather service. “Sometime around Jan. 3 or 4, wet weather will return.”

Rowe said the storm, dropping down from the Gulf of Alaska, could tap into tropical moisture and create an “atmospheric river,” which would likely generate more significant rainfall. In a typical year, California has between 10 and 15 “atmospheric river” storms which account for up to 50 percent of the state’s rainfall.

“It’s a bit premature to go off rainfall amounts at this time,” Rowe said. “It does look like it has the potential to bring light to moderate amounts. We can’t rule out locally heavy at this time. There are a lot of potential outcomes still out there.”

Any rain would be a welcome sight following one of the driest Decembers on record. This month is shaping up to go down as the second driest December in San Jose since records began in 1893, and the fourth driest in San Francisco dating back to 1849, according to the weather service.

San Jose is at 33 percent of its historic rainfall average for this date with 1.57 inches, while San Francisco is at 39 percent with 3.29 inches and Oakland is at 46 percent with 3.22 inches. This time last year, every one of those cities had more than 2.5 times as much rain.

The forecast also includes a chance of rain in Southern California, which has seen little to no rain since last winter. Rainfall totals for the majority of the southern part of the state are at less than 5 percent of normal or less, including Los Angeles’ .11 inches (3 percent), San Diego’s .09 (3 percent) and Santa Barbara’s .07 (1 percent).