Will smoke clear from the Sacramento area soon? Wind complicates air quality outlook
Air quality remains poor throughout the vast majority of California to start the week, including the Sacramento region, as some of the biggest wildfires in the state’s modern history continue to fill the sky with smoke.
Horrendous air pollution from the fires spiked in the immediate Sacramento area over the weekend. Near the capital, air quality index readings for particulate matter (PM 2.5) peaked above 200, the “very unhealthy” range, both Saturday and Sunday, according to SpareTheAir.com.
Max AQI was lower Monday, peaking around 170 throughout the region, and is forecast to gradually improve in the following few days. Early Tuesday, AQI readings varied throughout the area: Spare The Air said downtown Sacramento had a reading of just 90, in the “moderate” range, as of 6 a.m. At that same time, Arden Arcade and Roseville still had AQI levels above 150.
So, when might the smoke finally clear out?
That’s been a question on the front of Californians’ minds for the better part of the past month. And for the moment, the answer is still — excuse the pun — up in the air.
Local air districts at Spare The Air are currently expecting max AQI levels across Sacramento, Placer, Yolo and Solano counties to exceed 150 later Tuesday and again Wednesday, then possibly fall to the range of 101 to 150 Thursday and Friday. That range is deemed “unhealthy for sensitive groups,” such as those with asthma.
Recent National Weather Service forecasts for smoke activity show onshore winds have started to blow a good amount of the smoke away from Sacramento’s part of the valley, and are expected to continue to do so most of this week.
Until there’s widespread rainfall, Sacramento’s exposure to smoke is mainly at the mercy of wind patterns and how much smoke is produced by the numerous major wildfires burning in both Northern and Southern California.
Whether significant air pollution will stay comparatively low or surge once again after the onshore flow ends, currently predicted to happen by about the weekend, will depend on both the direction winds shift after that and how much containment firefighters can manage on multiple wildfires.
The Sacramento area’s bad air quality in the last three-plus weeks has come from multiple wildfires, but the worst of it since last Tuesday has come directly from the North Complex, which continues to burn in Butte and Plumas counties. Mid-last week, the West Zone of that fire complex (at the time, known as the Bear Fire) roared southwest from its origin point of Plumas National Forest toward Lake Oroville amid red-flag weather conditions: very dry and very gusty, according to the National Weather Service.
Burning at unparalleled speed, the deadly North Complex quickly produced an immense volume of smoke, with gusts above 50 mph pushing high concentrations of the polluted air west into the Sacramento Valley, especially last Tuesday and Wednesday. The sky turned orange as far as San Francisco.
Crews working to contain the wildfire complex made good progress over the weekend, but had braced for another round of gusty wind in the forecast Monday.
To fire officials’ relief, the “predicted gusty southwest winds and low humidity with periods of near critical fire weather conditions did not materialize” Monday, “nor will it over the next two days,” Cal Fire’s Butte Unit wrote in a Monday evening incident report for the West Zone of the North Complex. Fire activity didn’t flare up in the area, which is good news both for containment efforts and smoke output.
Scott Rowe, a meteorologist with the NWS Sacramento office, said last Friday that the onshore flow moving west to east was expected to continue through Thursday for California. He said the onshore flow can produce winds strong enough to push some of the wildfire smoke out of the region, but the extent of improvement this week will depend on whether fire activity also surges. A Delta breeze can also provide a more localized benefit for Sacramento.
Another NWS meteorologist from the local office, Emily Heller, told The Bee last week that it’ll take a more significant weather system, likely one that produces rain, to more definitively turn the tide on Northern California air quality.
The NWS isn’t currently anticipating widespread rainfall for Northern California, but says there is a slight chance of light showers Friday morning at Plumas National Forest, the site of the northern portion of the North Complex. Showers are also possible farther north in the valley, such as the Redding area, but aren’t predicted for Sacramento or for the immediate area of the North Complex’s West Zone.
Absent precipitation, smoke will disperse more slowly as fire crews gain containment on existing wildfires, but conditions should improve as weather cools down.
Smoke also came into Sacramento over the weekend from the southwest, from the 118,000-acre Dolan Fire burning in Monterey County, radar images from the NWS Bay Area office show.
As several recent Spare The Air forecasts explain, temperature inversions — warmer air falling on top of cooler surface temperatures — have been working to trap smoke near the ground in Sacramento. Nighttime temperatures were warmer than average early last week, in the low 70s from Sept. 6-8, but have cooled to the low 60s and upper 50s since last Friday. Lows close to 60 degrees are expected every night this week.
Minimal overnight cooldown was part of what made smoke conditions particularly bad last Wednesday: wind plus extreme wildfire activity plus temperature inversions let air pollutants from the North Complex linger near the surface.
Where has the smoke come from throughout recent weeks?
In mid-August, hundreds of minor and dozens of major wildfire incidents sprung up across Northern California as thunderstorms brought thousands of lightning strikes down from the greater Bay Area through the Sacramento Valley and into the Sierra Nevada foothills.
The predominant source of smoke for the capital region has shifted between four different massive wildfires.
First, in the second half of August, smoke blew west from the LNU Lightning Complex burning mainly in Napa, Sonoma and Lake counties to the east of Sacramento. (The LNU Complex is nearing full containment, but has burned over 360,000 acres to become the fourth-largest wildfire in California history.)
Then, amid shifting winds, smoke started entering Sacramento from the northwest, due to the massive August Complex burning near Mendocino National Forest in Tehama County. Several large fires merged with the August Complex over the weekend, and it is now by far the largest wildfire in recorded California history at over 877,000 acres (almost 1,400 square miles).
But last week’s severe wind gusts, which were felt in Sacramento and throughout the majority of Northern California, swept away much of the August Complex smoke, quickly replacing it with smoke from the West Zone of the North Complex.
Over the weekend and early Monday morning, polluted air in the Sacramento area has been a combination of stagnant smoke from the North Complex that stopped blowing in from the east and new smoke blowing from the southwest, primarily due to the Dolan Fire near Big Sur, amid onshore winds.
In general, if you can see or smell wildfire smoke, that means it is potentially hazardous to your health and you should avoid outdoor activity.
If you can smell smoke from indoors, there are measures you can take to fortify your home: replacing your air conditioning filter, using the “recirculate” feature on your AC unit, keeping doors and windows closed as much as possible and sealing any exposed cracks in those openings to help keep the polluted air outside.
This story was originally published September 14, 2020 at 10:36 AM with the headline "Will smoke clear from the Sacramento area soon? Wind complicates air quality outlook."
