Imagine a day with temperatures in the 90s and gale-force winds blowing in the San Mateo County hills.
Then imagine that someone or something ignites a fire, perhaps a sparking power line or an unattended campfire.
According to a survey of small towns in 11 Western states, such a scenario could trigger a disaster similar to the Camp Fire in Northern California last November that killed 85 people, burned 19,000 structures and destroyed the town of Paradise in Butte County.
The survey, undertaken by USA Today and the Arizona Republic before the Camp Fire and published in July, gave Woodside a rating on a one-to-five scale of 3.39 and Portola Valley a 3.63 rating for fire vulnerability the potential for death and destruction from a wildfire compared with 3.89 for the town of Paradise. (Towns closest to five on the scale are considered to have the highest vulnerability.)
The median wildfire risk in the study was 2.08 for more than 5,000 communities that were surveyed.
Portola Valley was also rated on a one-to-five scale at 3.09 and Woodside at 1.24 in a category called evacuation constraint, meaning the degree of difficulty in escaping a fire, compared with a median of 1.10 nationwide. Residents of towns with a rating closest to five have the greatest risk of being trapped.
The median age of residents, the number of residents with disabilities that would make it difficult to flee a fire, and the number of mobile homes that could catch fire easily were also factors in assessing the level of fire risk in the survey.
Jonathan Cox, the San Mateo County division chief with the California Department of Forestry and Fire Protection (CalFire), said he thinks the report could accurately reflect the degree of danger should a wildfire strike.
"Other parts of the state are as much or even more vulnerable than Paradise," said Cox, who was on the CalFire team at the Camp Fire. "The hillside areas on the Bay side of the county are highly vulnerable."
Red-flag warning days during hot weather with high winds occur much less often in San Mateo County compared with inland areas of the state, but if a deadly fire got started, the county's semi-rural communities could face some of the same vulnerabilities, Cox said.
"Early fires in forested areas at the turn of the century caused the founding of the county fire department," said Cox. "If a fire started in Woodside, it could burn up to the top of the ridge before it turned east toward the Bay."
Climate change is also making it more likely that the county could have a destructive wildfire. As temperatures rise, the cooling breezes that moderate periods of high temperatures are likely to taper off, making for more days when a fire could get started and spread out of control, Cox said.
The county has more firefighters and firefighting equipment in a smaller area than rural counties in the state, but that advantage could be lost if a fire wasn't contained in time and spread out of control during a period of hot weather and high winds, he said.
Under the most hazardous conditions, such as during the Camp Fire, wildfires can spread at the rate of 1 acre per second, making them virtually impossible to stop after they break out, he noted.
"If a fire burns in normal conditions, we are resource-rich in San Mateo County to combat it," Cox said. "If it burns in abnormal conditions, that's where we are the most concerned."
The county and local towns and cities can take a number of measures in advance of need, including hiring more firefighters and closing parks and outdoor areas during critical fire weather to combat the threat, Cox said.
Local agencies are working to respond to the challenge, according to Woodside Fire Protection District Fire Marshal Denise Enea, who is one of the officials charged with leading the local push toward fire prevention and ensuring the safe evacuation of residents if necessary.
Fire districts and departments are starting to use computerized tools to look at the number of homes in an area and determine how much traffic streets could handle if residents were trying to access them all at once in an effort to escape, Enea said.
"We have a special situation in the hills where some of our roadways are only one way and, if two cars meet, you come to a standstill," she said.
Officials are promoting evacuation drills so that neighborhoods can practice in advance of the real thing, Enea said.
The fire district is also developing online interactive maps that people could access during an emergency to find where fire hydrants, generators and emergency supplies are located, she said.