Strong winter storm to drench North Coast, raising slide risk in burn scars

A powerful winter storm expected to dump half a foot of rain or more on the North Coast beginning Tuesday has raised the risk of flooding around the region, as well as concerns about potential debris flows in the area’s massive wildfire scars.

Emergency officials are urging residents to be aware of their surroundings and to remain tuned in to emergency alert systems in case trouble begins once the atmospheric river arrives overhead, bringing 4 to 6 inches of rain across the region.

A flash flood watch is in effect from Tuesday afternoon to Thursday afternoon, along with a high wind warning, running from Tuesday evening through Wednesday afternoon. National Weather Service meteorologist Brayden Murdock said periods of wind gusting to 60 mph, even in the valleys, were likely, raising the possibility of downed trees and power outages.

“It’s going to be raining sideways with some of these gusts,” he said.

Murdock also said residents should expect to see surface flooding in low-lying areas and across areas that routinely flood.

Officials urged vigilance especially for those who live or work in or near the most severely burned areas of last year’s Walbridge and Glass fires, where rain arriving in heavy volumes could unleash dangerous amounts of earth, rock, trees and other debris as it heads downhill.

This mass of stuff, channeled into a streambed, can travel more quickly than it can be outrun. It also can amass and then explode with deadly force.

“When water’s trying to go downhill, and something gets in its way, it’s going to find a way to go around or through, or just bust through and take everything with it,” said Russian Riverkeeper Executive Director Don McEnhill.

Some, like Sonoma County Fire District Chief Mark Heine, even suggested residents of those areas find alternate places to stay Tuesday night, during the heaviest rainfall.

“I just don’t think it’s worth the risk,” Heine said.

Others recommend they at least have a “go bag” at the ready.

The incoming storm, the wettest of the winter so far, is forecast to deliver an outsized payload in a rain season that has been perilously dry. It comes a week after spring-like temperatures eclipsed heat records over two days, reaching 80 degrees in Santa Rosa.

In the months since the fires occurred, grass and light groundcover have regrown in some areas. The Walbridge fire burned nearly 55,000 acres in steep, remote territory west of Healdsburg beginning Aug. 17, and the Glass fire, which stretched across more than 67,000 acres of Sonoma and Napa counties, started Sept. 27.

But the flames left severely scarred canyons and steep slopes that may still be resistant to absorbing heavy rainfall, and thousands of burned and unstable trees that could topple if the ground starts to shift.

Based on surveys conducted of each fire scar, Glass, Walbridge and related Meyers fire zones, heavy rainfall of at least 0.4 inches in 15 minutes, 0.6 inches in 30 minutes or 1 inch in one hour could trigger a debris flow, the surveys found. The threshold is even lower in the scorched mountains above Santa Cruz, where up to twice the amount of rain is expected, raising particular fears about that region, Murdock said.

In and around Santa Rosa, officials are especially concerned about neighborhoods east of Calistoga Road around Alpine Valley, Skyhawk, Pythian and Melita roads, where damage from the Glass fire was hit and miss. Above many of the occupied homes sit steep, burned slopes, city spokeswoman Adriane Mertens said.

Fire crews would be out in those areas on Tuesday delivering information to anyone they encountered and ensuring that folks were aware of upcoming weather conditions, she said.

Santa Rosa city staff and Catholic Charities workers were out on Monday trying to persuade members of the homeless community, particularly those around the Prince Memorial Greenway and Santa Rosa Creek, to accept shelter beds for the duration of the storm. They also are accepting donations of new tarps, sleeping bags, rain gear and socks at the Homeless Services Center, 600 Morgan St., between 6 a.m. and 5 p.m. daily this week.

At the center of the Walbridge fire scar, meanwhile, lies the tiny postal stop called Venado, which routinely registers some of the highest rainfall in Sonoma County — and the entire West Coast. It’s there on Mill Creek that that some of the worst fire damage occurred last summer, leaving scorched canyons vulnerable to heavy runoff and home sites still littered with the hazardous debris left when the fire ran through.

Properties whose owners did not immediately respond to requests from the county for permission to clear the land of hazardous wastes have, in some cases, been overridden because of proximity to vulnerable creeks, leaving crews scrambling to try to do what they could in the past few days to prevent toxins and garbage from running off site.

Workers from the Community Soil Foundation, working under contact to the county, were out on Monday trying to lay down straw wattles, tarps and jute blankets to do what they could to limit runoff this week.

“The amount of water that they’re saying is coming from this upcoming atmosphere river is significant,” said Paolo Tantarelli, co-founder of the foundation.

Fire chiefs also were meeting to discuss what preparations could be made in advance of the storm, while emergency officials laid plans for patrolling burn areas and monitoring stream and water gauges.

This burn severity map shows areas at risk for flooding, debris flow and rockfall in the Walbridge fire burn zone.

In Monte Rio, firefighters spent the day scouting potential vulnerabilities to eliminate before the rain and wind arrive: They cut down dead and decaying limbs, and made sure their chainsaws would remain fueled for the onset of the storm, said Chief Steve Baxman,

Tuesday, he said, “We’ll check them during the morning and patrol during the storm.”

Firefighters also went around to talk to neighbors, making sure residents planned to secure loose items on their properties and that the backup generator at local stores were ready to kick in if the strong winds take out any power lines.

Baxman said his volunteers will be ready to respond to reports of downed power lines or debris flow in the Monte Rio area.

“We’ve done it once or twice,” he said, downplaying decades of experience with such storms. “The smaller places have to take care of themselves.”

This burn severity map shows areas at risk for flooding, debris flow and rockfall in the Glass fire burn zone.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. Staff Writer Kaylee Tornay at 707-521-5250 or kaylee.tornay@pressdemocrat.com.