A winter-like storm distanced itself from the Bay Area on Wednesday, but the imprint it left behind won’t fade quickly.
“This one,” National Weather Service meteorologist Roger Gass said Wednesday, “pretty much overperformed.”
Indeed, October storms in the region rarely have carried the punch that this one brought, especially in the South Bay. San Jose received 1.52 inches of wet stuff since the storm’s start on Monday, pushing the city’s total so far in October to close to 2½ inches. According to the weather service, that already makes it the second-wettest October on record, behind only 2009.
By Wednesday afternoon, the rain was expected to end, Gass said. Occasional isolated light showers continued to fall Wednesday morning — .08 inches dropped in Oakley between between 2 a.m. and 8 a.m., the weather service said — but the low-pressure system from the Alaskan gulf was moving east and Wednesday’s moisture came from the tail end of the system.
It still was causing weather headaches in the Sierra Nevada, where a winter storm watch remained in effect until 11 a.m. Wednesday. Snow fell Tuesday starting between about 5,500 to 6,500 feet of elevation, according to the weather service.
The rain that pelted the region came down considerably lighter on Tuesday than it did 24 hours earlier, when the storm first hit. At 6 a.m. Wednesday, the 24-hour rainfall totals in the region showed .12 inches on Mt. Umunhum in the Santa Cruz Mountains; .16 inches on Mount Diablo; .04 inches in Fremont, .03 inches in downtown Oakland.
San Jose did not receive any measurable rain Tuesday, but the 1½ inches it had on Monday was the third-highest total for any October day since 1897, when records in San Jose first were kept. The weather service initially said it had been the second-biggest rain day ever in October for San Jose but that it later corrected itself.
According to the weather service, the only October days that saw more rain in San Jose were in 2009 (2.33 inches) and 1962 (3.22). Both of those downpours also came on Oct. 13.
Those figures are notable for an area that often misses out on heavy rain when storms pass because of a meteorological phenomenon called the “shadow effect” that’s caused by the Santa Cruz Mountains. Moist air from the Pacific Ocean rises over the mountains and loses much of its precipitation as the air heats up after going over them, often leaving San Jose dry.
“This was more of a cold upper-level low, resulting in rain showers, so that area was not affected as much by it,” Gass said of the shadow effect. “That’s as opposed to what happens with an atmospheric river affect when that rain shadow is heavy.”
Overall, other 72-hour rain totals recorded by the weather service since the storm began Monday showed 2.33 inches in the Santa Cruz Mountains; 2.2 inches in downtown Oakland, 2 inches on Mount Diablo, 1½ inches in Fremont, and 1¼ inches in Hayward.
The region emerged mostly unscathed. Residents in the Pickett Burn area of Napa County received a flash flood warning about 4 p.m. Monday night that remained in effect for about an hour. The California Highway Patrol also closed the transition ramp from northbound Interstate 880 to eastbound Interstate 980 in Oakland about that same time. The closure lasted about 2½ hours.
The dry-out began Wednesday with some cooler air still present and clouds still covering the region. The hottest places inland were expected to climb into the low 60s. Those temperatures are expected to build into the seasonal norm of the 70s as the weekend arrives.
