SONOMA COUNTY (CBS SF) -- A red flag warning has been issued for parts of the North Bay this weekend for high fire danger due to gusty winds, hot weather and low humidity, according to a statement from the Sonoma County Sheriff's Office.
The warning runs from 11 a.m. Saturday through 8 p.m. Sunday.
During that time residents of northern and eastern Napa and Sonoma counties, as well as the Diablo Range, can expect any fires that start to spread quickly, leading to significant threats to life and property.
Area residents are advised to avoid lawn work, driving on grass, campfires or fireworks. Lit cigarettes should always be disposed of safely.
Elevations over 1,000 feet in the affected area are at the greatest risk, according to sheriff's deputies.
Wildfire concerns were being voiced across the region due to the expected hot weather this weekend.
A high pressure system building off the Northern California coast will send both temperatures and the threat of wildfires soaring, forecasters predicted.
The National Weather Service said Saturday would be hottest day with inland temperatures climbing into the 90s and triple digits. The stifling heat will be joined by winds gusting to 30 mph and humidity in the teens — a set of conditions most feared by firefighters.
A fire weather watch has been issued for the Bay Area by the weather service for late Saturday morning through Sunday evening.
"The areas of greatest concern will be located in higher terrain of northern and eastern Napa and Sonoma county as well as throughout the Diablo Range," the weather service warned. "Any fire starts may spread rapidly in these conditions."
The weather service asked residents to "avoid activities that may lead to fire ignition, including lawn work, driving on grass, tossing cigarettes, lighting campfire or fireworks, especially during Saturday and Sunday afternoons."
During a ride along with Alameda County firefighters on Friday, authorities pointed out which houses in Castro Valley stood a better chance of surviving a fire and which ones didn't.
"It's not well managed at all," said Alameda County Fire Division Chief John Walsh, pointing at a house with no defensible space.
With the anticipated combination of heat, low humidity and high wind, the red flag warning issued for this weekend means it is dangerous for houses surrounded by dry fuel.
"If the homeowner provides good defense, we can come in and provide a good offense," said Alameda County Fire Capt. John Hill.
That said, they still don't want people to fire up the lawn mower this weekend.
"It's too late to do work when you have these red flag warnings. We don't want you to do too much vegetation removal," said Walsh. "Right now, any spark in these conditions can ignite a fire."
Firefighters said it's also important for families to talk about an evacuation plan.
"A lot of the urban interface homes that we deal with have no access roads. So when people are trying to get out and we're trying to get in, it creates a bottle neck affect," explained Hill.
He said that's why people should follow evacuation warnings. Depending on the location, firefighters recommend defensible space of up to 300 feet.
The stagnant air mass forced the Bay Area Air Quality Management District to issue the first and second Spare the Air smog alerts of the year for Friday and Saturday.
Light winds combined with high temperatures and exhaust from motor vehicles are expected to cause unhealthy ozone accumulation in the Bay Area, according to the Air District.
"Emissions from the millions of vehicles on Bay Area roadways in combination with hot temperatures will create unhealthy air quality in our region," Jack Broadbent, executive officer of the Air District, said in a statement.
Broadbent called for commuters to find alternatives to driving alone to help the area reduce the amount of transportation-related pollution.
Spare the Air Alerts are issued when ozone pollution is forecast to reach unhealthy levels. Ozone, or smog, can cause throat irritation, congestion, chest pain, trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema.
Temperatures in San Jose will likely reach the upper 90s and in areas from Redwood City to Cupertino temperatures will reach up to 100 degrees, according to the National Weather Service.
Officials said to avoid strenuous outdoor activity, stay in cool locations and drink lots of water. The city's park service will open several cooling centers to assist residents during the heat wave.
The centers will operate Saturday from 1 p.m. to 9 p.m. at Bascom Community Center, Camden Community Center, Alum Rock Youth Center, Roosevelt Community Center and Seven Trees Community Center.
The advisory is in effect from today through Sunday, and residents are asked to avoid any activities that could spark a fire, such as barbecuing, tossing cigarettes and having campfires.
Meanwhile, the weather services issued an excessive heat watch for Sacramento and the Central Valley. Temperatures as high as 108 were forecast for over the weekend.
"There is potential for heat-related illness to humans, pets, and livestock with long outdoor exposure," the weather service said.
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