Storm door opens in San Francisco — what will the rains bring?

‘Come Monday, fire season in Northern California should be done’

A succession of storms will bring much-needed rainfall and cooler temperatures to the Bay Area this week, capping off the hottest summer ever recorded in California.

The first of the storms arrived Tuesday night, bringing gusting winds and chilly temperatures. Showers are expected to continue throughout the week, culminating in what meteorologists call an atmospheric river — or a column of condensed water vapor — projected to drench the Bay Area this weekend.

“The storm door is officially open,” the National Weather Service wrote on Twitter. “A series of wet systems are expected to impact the region throughout the week and into the weekend. Still some uncertainty in the long term, but more rain is on tap.”

But while the state is thirsty for precipitation and residents are desperate to put this year’s wildfire season to rest, the storms have local agencies bracing for potentially hazardous conditions following an extended dry period and prompting scientists to question if climate change is at play.

On Wednesday, PG&E reported that over 3,000 customers across the Bay Area experienced power outages as the first showers rolled in, with most outages concentrated in the Peninsula.

“During a dry season, and especially amid the current drought affecting California, dust, dirt, salt and other substances accumulate on power lines,” said Tamar Sarkissian, a spokesperson for the public utility. “When light rain or mist arrives after a long dry spell, it can turn this mixture into mud, which conducts electricity. This can damage electrical equipment, potentially resulting in pole fires and outages”

PG&E is deploying what it calls an “all-hands-on-deck approach to storm readiness,” expanding its pole washing program to prevent outages and closely monitoring the incoming storms.

The National Weather Service cautioned drivers of slick roads, noting that oil accumulates on roadways during the dry season and gets reactivated with the first big rainstorm.

Some San Franciscans were prepared for the precipitation that hit The City on Wednesday. (Kevin N. Hume/The Examiner)

Some San Franciscans were prepared for the precipitation that hit The City on Wednesday. (Kevin N. Hume/The Examiner)

Still, the wetter weather has Californians rejoicing as models suggest there could be enough rainfall to effectively end this year’s fire season and improve drought conditions.

If the forecast holds? “Come Monday, fire season in Northern California should be done,” said Michael Anderson, state climatologist with the California Department of Water Resources. “Things will be pretty soggy.”

But he noted that, if the rain falls with a certain degree of intensity, it could also trigger dangerous debris flows in areas scarred by wildfires. Locations downstream or downhill from wildfire burns are especially vulnerable to flowing debris as burned soils can be as water-repellent as pavement, according to the National Weather Service. As a result, less rainfall is required to generate a flash flood.

When heavy rains trailed the Thomas Fire near Santa Barbara in early 2018, powerful debris flows leveled houses and killed more than 20 people.

The early season storms are also prompting climate scientists to question if this blast of precipitation is related to the warming climate. “This is a little more evolved of a weather pattern than we might expect this early in the season,” said Anderson, adding the rainfall totals are something we don’t normally see in October. “Again, you get that, ‘Hmm, we haven’t seen this before.’”

That said, it’s hard to link a singular weather event to the changing climate. Anderson said this storm is born of a unique set of circumstances, including a historic drought and wildfire season, and two successive years of La Niña — a weather pattern that occurs in the Pacific Ocean and could spell more severe droughts in the West and extreme hurricanes in the Atlantic.

Even so, the atmospheric river expected to drench the region this weekend is “as big as anything we’ve seen in a long time,” said Anderson. “We’re not sure how it’s going to play out. But there’s going to be a whole lot of learning going on.”

jwolfrom@sfexaminer.com

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