The state fire agency has determined that “dangerous fire conditions” continue to exist on the Peninsula, and that the danger will require the staff of six trucks to remain in the area.
“It’s phenomenal how dry it is,” said Christopher Burt, weather historian for Weather Underground. “It’s tinder-dry up there on the surface.”
This year stands out as being particularly hazardous in terms of the threat from wildfires, officials note. So far in 2013, the San Mateo-Santa Cruz Cal Fire unit has responded to 344 blazes within its area of responsibility, according to Division Chief Angela Bernheisel. And those 344 fires are responsible for considerably more destruction — scorching 152 acres of land, or 360 percent more acreage than in 2012. Last year, 296 fires in the unit’s coverage area burned only about 33 acres of land.
Ninety percent of the fires that break out each year are human caused, the vast majority of which are accidental, Bernheisel said. Lightning is the most common natural cause, The oldest available climate data in the region is taken from a weather station in downtown San Francisco that has been in operation since 1849. The single driest year in the 164 years of continuous precipitation records saw nine inches of rainfall. So far in 2013, San Francisco’s weather station has recorded just 3.95 inches, while San Francisco International Airport has received 2.65 inches.
“It’s possible there will be five inches of rain in the next six weeks,” Burt said. “But current models are not looking at rain until the end of the month.”
If a sudden downpour occurs, it might look something like the large storm that hit the region in 1995, he suggested.
Generally, the Peninsula is about 10 percent drier than The City annually —especially the Peninsula cities along the Bay’s shore.
Rainfall typically begins to hit the Bay Area sometime in late October or early November, when a low-pressure system from the Alaskan coastline replaces the high-pressure dry system that blocks storms from hitting the California coast, Burt said. Typically, the low-pressure system starts steering storms toward the coastline, creating the winter rainy season, Burt said.
Rainfall has been low since 2011 — averaging about 65 percent of the normal precipitation for the area, according to the National Weather Service. “Normal” precipitation is based on a 30-year average.
It’s very difficult to determine whether or not the dryness has been due to climate change, or is just a part of the typical weather pattern, Burt said. That’s because it’s normal to have two- or three-year periods of drought-type conditions.
“It happened in 1975-1977, and again from 1987-1991,” he said. However, Burt said that it’s rare to have three dry years in a row, like the Bay Area is experiencing now.
The cost of extending Cal Fire staffing through Monday is $126,000. Depending on weather conditions, Bernheisel said she could extend that deadline.