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| Smoke from the Northern California wildfires was impacting the air quality in the Lake Tahoe Basin on Friday, Aug. 6, 2021. |
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'Completely white': Ash, smoke fall on Tahoe Basin
San Francisco Gate
Fri August 6, 2021
Area: Sacramento, Stockton, Modesto
Winds pushed smoke from Northern California's Dixie Fire to the south Friday, choking the Lake Tahoe Basin with toxic air.
The mountains ringing the lake that straddles the California-Nevada border were hidden behind a curtain of smoke, and there were reports of ash falling from the sky throughout the Truckee-Tahoe region.
"I definitely can't see across the lake, whereas normally I would be able to see the mountains," said Andy Plascencia, who was speaking to SFGATE from Tahoe Park Beach on the West Shore. Plascencia, 19, grew up in Tahoe and has worked at the beach for the last four summers. "Right now it just looks completely white, kind of like the ocean."
As of mid-day Friday, the air quality forecast for North Lake Tahoe was "unhealthy," but earlier in the morning, air quality in the Lake Tahoe Basin had reached the worst indicator, "hazardous," according to AirNow, a government website that tracks air quality.
"You can smell the smoke, and this morning, there were also some ashes on my car," Plascencia said.
The first smoke arrived Thursday night as a low pressure system moved across Northern California and southern Oregon, shifting the winds from a southwesterly direction to northeasterly, National Weather Service meteorologist Marvin Boyd said.
The winds changed direction as the Dixie Fire exploded in size and pumped out towering clouds of smoke, pushing the sooty air to the south.
"With the strong winds on Thursday created extreme fire conditions and the Dixie Fire put out a lot of smoke ... then the winds shifted and that's all being pushed southeast," Boyd said.
Boyd said visibility was impacted in Reno where he works. In the Reno area, the smoke seemed to put an orange filter on the light and visibility and blotted out the mountains on the horizon.
"This morning the sun was just really dull red circle in the sky," he said.
When smoke impacts air quality to such extreme levels, authorities in Lake Tahoe receive an influx in calls from visitors and residents, said Lisa Herron, spokesperson for the U.S. Forest Service Lake Tahoe Basin Management Unit.
"[The smoke] is a direct impact of the conditions we're seeing," Herron said. "We're back in a severe drought. Conditions are really dry. Fuels are really dry. Yesterday, we had a red flag warning."
Herron said the wildfire smoke today is bad, but she remembers air quality in Tahoe during Yosemite's 2013 Rim Fire as being much worse. "During the Rim Fire, that was terrible," Herron said. "That was probably the worst I've seen it. I remember distinctly because it was so bad. We had about three weeks of solid smoke in the basin from that."
Boyd said it's difficult to determine exactly when the smoke will clear. "I expect we could possibly start to see some relative improvement today, but honestly, it's not going to be until tomorrow and Sunday and especially Sunday when west and southwest winds pick back up and push the smoke back toward the fire."
A Twitter user shared a screenshot from the website Purple Air at 7:42 a.m. Friday showing some locations with air quality readings in the 300s, 400s and 500 and higher.
The Air Quality Index operates, typically, on a scale from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. An AQI value of 50 or below represents good air quality, while an AQI value over 300 signals hazardous conditions.
PurpleAir’s numbers are measured in real-time (averaged over the previous 10 minutes). AirNow’s figures — which are based on Environmental Protection Agency standards — are calculated using a complex algorithm that "uses longer averages during periods of stable air quality and shorter averages when air quality is changing rapidly." Results are updated hourly but delayed compared with PurpleAir.
The Dixie Fire grew more than 100,000 acres in 24 hours, with its total burn area increasing from 322,502 acres Thursday to 432,813 acres Friday morning, making it the third largest blaze in state history. Started near Cresta Dam in the Feather River Canyon on July 14, the blaze is burning about 280 miles northeast of San Francisco and is spread across four counties: Plumas, Butte, Lassen and Tehama.
The fire has pumped out multiple massive pyrocumulonimbus clouds since it first sparked in July.
"I can tell you conditions are ripe right now for pyrocumulonimbus cloud development," said Mitch Matlow, a spokesperson with the multi-agency team managing the fire. "I’m looking out my window at one right now, which is very large."
These massive, mushroom-shaped clouds of hot, smoky air towering thousands of feet into the sky are caused by a natural source of heat such as wildfires, according to NASA. Rising warm air from the fire carries water vapor, ash and smoke up into the atmosphere, forming clouds.
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