Storm to potentially slow the start of the fire season in parts of the Bay Area. How much rain could we have?
A late spring rainstorm is expected to blanket North Bay with up to a half inch of rain over the weekend, potentially wetting fuels enough to delay the start of the fire season.
A weak cold front is expected to come in from the west Saturday evening through Sunday with a fair amount of moisture, concentrating the bulk of the storm just over North Bay and into Oregon, according to the National Weather Service. There won’t be much of a chance of snowfall in the Sierra Nevada, like in the case of storms descending from the Gulf of Alaska. The North Bay hills could get about a half inch of rain while the North Bay valleys could get about a quarter inch. The East Bay is expected to receive a few hundredths of an inch, the SF Peninsula could receive a few hundredths to a tenth while the Santa Clara Valley is expected to receive a trace of a hundredth of an inch of rain.
“It’s good rain, especially for North Bay. We’re expecting a quarter of an inch – that’s enough to slow the peak fire season in this area,” said NWS forecaster Ryan Walbrun. “In East Bay and South Bay, when you’re talking about a tenth less, it won’t have any impact on the fuels.”
Sonoma County could see light precipitation early Saturday evening while the rest of the Bay Area is expected to see rain Saturday evening through Sunday morning before the storm dissipates. Although temperatures are expected to be below average due to cloud cover and overland flow, the storm is not expected to be particularly cold due to the lack of cold air associated with the system. Along the coast and bays, highs are expected to be between the 65s and 70s, while the warmer interior valleys could see temperatures in the 70s to around 80s. from the 50s.
“We generally expect one to three weak systems in June,” Walbrun said. “It’s not unusual, but obviously we had a dry year. We will accept all the rain we can, especially in the North Bay.
Still decent chances for heavy rain over North Bay this weekend. Those chances decrease a little elsewhere, although very light rain or drizzle can at least wet the ground in spots. #cawx pic.twitter.com/p0yKTaiSTe
— NWS Bay Area 🌉 (@NWSBayArea) June 3, 2022
Dry weather is expected after the storm, along with a gradual warming trend with above average temperatures around mid-June. No other storms are on the horizon for the next seven to ten days in the Bay Area.
Despite atmospheric river storms in October and December and rains in March and April, the fuels remained relatively dry. The Sierra Nevada snowpack, which accounts for 30% of the state’s water supply, fell to one of its lowest levels in decades, reaching 7% of normal on Thursday.
“We do get rain especially for places like San Francisco in June, but not in large amounts, so that would put us on the right track,” Walbrun said. “It’s normal to have a weak weather system in June. What would be abnormal is to have no rain in June. San Francisco airport for the month of May received a trace of rain; a normal May would get about half an inch.
The US Drought Monitor also reported on Tuesday that about 98% of California is in “severe drought,” a 69% increase from about three months ago. About 60% of the state is in “extreme drought,” the second most severe stage, up from 7% three months ago. Extreme drought has spread to the North Shore and all nine counties in the Bay Area are currently experiencing severe drought.
National Interagency Fire Center Predictive Services also released its significant outlook for wildfire potential on Wednesday from June through September, showing fire activity increased in parts of California in May. The state is expected to see significant above normal fire potential through September. California received below normal rainfall for the month of May. The drought is expected to worsen over the summer months, but not as severely as in the past two years due to less potential for long hot spells. Fuels will continue to become more flammable, starting at lower altitudes and moving up between June and July.
“Much of the fuel analysis shows the grass, branches and trees are basically as dry as possible for June,” Walbrun said. “When it rains on Sunday, it will temporarily reduce the fire danger. Everything is still preparing for a busy fire season in July, August and September.