Weather conditions aid firefight but diminish air quality for Sonoma County residents

The buildup of smoky air in North Bay communities since Sunday represented yet another health threat for local residents, but for firefighters, it signaled the persistence of calmer conditions that have allowed crews to gain ground on week-old wildfires.

The dropoff in wind in the hills, however, has led to smoke accumulation in more settled valleys across Sonoma County and the greater Bay Area, posing a threat to children or residents with health risks, especially if they’re outside for a prolonged period or choose to exercise in the open.

Th air quality index rose as high as 152 on Monday, well above the 100 federal health standard for healthy air, according to the Bay Area Air Quality Management District. A Spare the Air alert remains in effect through Wednesday, banning any wood-burning or fires both inside and outdoors.

Pollution levels for the past two days have followed a similar pattern, with smoke settling more heavily across the region in the morning before the arrival of afternoon gusts.

A lower coastal marine layer, the air mass that forms over the Pacific Ocean and pushes inland as fog, also has put a ceiling on the hazy buildup, trapping smoke closer to the surface while keeping vital moisture away from fires burning higher in the North Bay mountains.

Atmospheric models predict that layer could begin rising later this week and bring blankets of fog that are more typical this time of year, a sign that more progress could be made with moisture reaching higher altitudes of the LNU Lightning Complex fires.

“When you have that inversion, temperatures are higher (at higher elevations),” said Duc Nguyen, a meteorologist with the Bay Area Air Quality Management District. “You still had very dry air yesterday even though we see increased moisture along the coast. But from the perspective of firefighting, we didn’t have much change because of the level the fires are burning.”

Thick, sooty air continued to blanket the North Bay on Monday as changing weather conditions dictated how firefighters attacked multiple lightning-sparked wildfires that have been burning for a week across the region.

The poor visibility made it harder to get aircraft off the ground on Sunday, Cal Fire incident commander Sean Kavanaugh said during a press briefing Monday.

Those conditions did, however, make it easier for the nearly 2,000 firefighters battling the regional blazes to strengthen fire lines and bulldozer paths. A similar plan of attack was deployed Monday, officials said.

“We’re taking advantage of the weather,” Kavanaugh said. “We can’t pass up those situations and those opportunities.”

Prevailing winds have pushed smoke from California’s wildfires as far away as the Midwest, with smoke visible in Kansas, the National Weather Service reported.

The weather service ended a red flag warning Monday morning for the Bay Area and parts of the Central Coast, several hours before the expected expiration of an alert tied to potentially dangerous storms featuring dry lightning and gusty winds.

Cindy Palmer, a National Weather Service meteorologist, said a number of lightning strikes were reported across Northern California and on the eastern edge of the LNU Lightning Complex Sunday night and into the early morning hours Monday.

But the bulk of the activity was in the Central Valley and the Sierras. The threat to the North Bay had passed.

Isolated lightning strikes and light showers were an outside chance, Palmer said, but drier conditions prevailed.

Modeling showed typical weather patterns for this time of year would arrive this week, but there was “enough disagreement” among area meteorologists to rule out red flag conditions returning, she said.

“We’re watching it to see if we’ll need something,” Palmer said, of another potential warning.

You can reach Staff Writer Yousef Baig at 707-521-5390 or yousef.baig@pressdemocrat.com. On Twitter @YousefBaig.