MONTEREY — High winds with forecasted gusts of up to 70 miles an hour at the highest peaks are set to buffet the Bay Area starting Sunday evening, a grave warning for firefighters who have been aided by favorable weather the past week.
The kind of cold, humid air that blanketed much of the San Francisco Bay on Sunday morning is set to dry out starting around 7 p.m. Sunday evening, when winds will switch from blowing into the Bay from the sea to flowing out of the dry valleys and into the ocean.
Commonly referred to as Diablo Winds, these offshore gales were set to be at their strongest during the middle of the night Sunday. They’re expected to die down slightly around 7 a.m. Monday morning, but not before completely sucking the humidity out of the area.
National Weather Service Meteorologist Duane Dykema said Sunday humidity values were at their highest, measuring 80 to 100% humidity across much of the area. If a fire starts Sunday before 7 p.m., Dykema said the fire would likely not spread very far and would be more easily contained given the amount of moisture in the air.
“But when those offshore winds kick in tonight, we’ll see humidity plummet very rapidly,” Dykema said, adding that humidity values will drop down to 17 to 20%. “It’s an abrupt change.”
Such a precipitous drop in humidity coupled with high winds are two of the three ingredients necessary for quickly-spreading fires, Dykema said. The third is that fire fuel needs to be dry.
“For us, typically the fuels are always dry because of our Mediterranean climate,” Dykema said. “We’ve had no wetting rains to soak into the fuels. This year they’re as dry as they’ve ever been. For rapid fire spread you need dry air. There’s definitely the potential for explosive fire growth today and tomorrow.”
In the 12-hour period between 7 p.m. and 7 a.m. Sunday to Monday, forecasters predicted sustained winds between 20 and 35 miles per hour with gusts around up to 50 miles an hour in general. At the highest peaks like Mt. Diablo and Mt. Tamalpais gusts could hit 70 miles per hour.
“Even winds much lighter than that would be dangerous,” Dykema said.
But despite the increased fire danger from wind, the hot weather appears to be staying away. Temperatures are warmer than average this week, Dykema said, with values across the Bay Area predicted between the 70s and lower 80s.
At night, drier-than-normal air masses caused by the Diablo Winds will make rapid cooling at night possible, meaning chilly nights in the valleys from Monday night to about Wednesday night. North Bay valleys could see temperatures dipping into the 30s, while Santa Clara Valley is likely to drop into the low 40s and upper 30s.
“As you get closer to the Bay, San Jose for example, the warmer the night,” Dykema said.
As for rain, Dykema continued the honored tradition of dashing hopes and said there is not likelihood of rain in the next 7 to 10 days, tough he said a decent rain is usually expected around late October and early November.
Air quality across the Bay Area remained Good Sunday, according to AirNow.gov, and is forecasted to remain Good to Moderate throughout the week.
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Author: Aldo Toledo