Smoke from California's Mosquito Fire flooded the Lake Tahoe basin on Thursday.

LATEST Sept. 8, 5:50 p.m. A heavy blanket of smoke choked the Lake Tahoe basin on Thursday evening as the Mosquito Fire continued to burn through parched terrain and pump out massive amounts of smoke. 

National Weather Service forecaster Hannah Chandler-Cooley said westerly winds pushed the smoke from the fire toward Tahoe. 

“It’s spreading right over Lake Tahoe, and directly south of the fire through most of El Dorado County,” she said. 

Sept. 8, 1 p.m. Smoke from California’s Mosquito Fire near Foresthill flooded communities east of Sacramento in the Sierra Foothills on Thursday afternoon, resulting in hazardous air quality.

AirNow, a site run by the Environmental Protection Agency, showed hazardous air quality levels in Auburn, Cameron Park and El Dorado, as of 1 p.m. Placerville showed unhealthy air quality, and El Dorado Hills very unhealthy. 

Air quality on Lake Tahoe’s South Shore was unhealthy and moderate, according to AirNow. The weather service said the Tahoe area could see a push of smoke later in the day. 

The air quality in Sacramento was good as of 1 p.m., but the Sacramento Metro Air District warned of unhealthy levels later in the day. 

Here is the updated smoke forecast for #Norcal. Smoke from the #MosquitoFire will continue to impact parts of #NorCal over the next couple days. For your local air quality forecast visit https://t.co/LRRlZa8Gmk for the latest near surface smoke loop https://t.co/DLEkoh4Nnz #CAwx pic.twitter.com/dZX4eCLhDq

The Bay Area Air Quality Management District issued an air quality advisory for Friday, as smoke from the Mosquito Fire could impact the region. 

Because pollutant levels in the nine-county Bay Area are not expected to exceed the national 24-hour health standard, a more severe Spare the Air Alert was not issued. “Smoky, hazy skies may be visible and the smell of smoke may be present,” the district said.

Smoke from the Mosquito Fire filled the air at Lake Tahoe on Wednesday. 

Sept. 8, 7:23 a.m. Air quality on Lake Tahoe’s South Shore deteriorated early Thursday as smoke from California’s Mosquito Fire burning near Foresthill pushed east.

Weather radars showed smoke over the Tahoe Basin on Thursday morning, said Mark Deutschendorf, a meteorologist with the National Weather Service office in Reno.

“We’ll probably see a few hours of improvement, but then with the activity of the Mosquito Fire, most of the Tahoe basin will see a push of smoke in the afternoon,” Deutschendorf told SFGATE on the phone.

Light westerly winds will nudge the sooty air east  in the afternoon, but Deutschendorf said overnight winds will shift north to northeast, kicking the smoke into the Central Valley and the west slopes of the Sierra foothills.

Here is a rough idea on what we can expect for smoke + haze across western Nevada and northeast California through 3pm this afternoon. Note: The fire in Hazen, NV is included but the new Barnes Fire in east Modoc is not yet in the model. Visit https://t.co/0i8pER1rle #nvwx #cawx pic.twitter.com/zvO2V5AxK0

The Purple Air website showed unhealthy air quality levels around South Lake Tahoe with Air Quality Index readings over 190 just before 7 a.m. on Thursday, while the site revealed levels that are considered moderate to unhealthy for sensitive groups on the North Shore. AirNow, a website run by the Environmental Protection Agency, showed unhealthy air quality in South Lake Tahoe with AQI readings up to 175.

Towns east of Sacramento, such as Auburn, were flooded by smoke from the Mosquito Fire on Thursday.

The Air Quality Index, or AQI, is based on a scale from 0 to 500. The higher the AQI value, the higher 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. Both Purple Air and Air Now use this scale. AirNow, a website run by the Environmental Protection Agency, indicated that air quality in the Tahoe area is moderate.

Air Now uses AQI readings from highly accurate sensors monitored by the EPA. Many of the Purple Air sensors are installed by everyday people and connected to the company’s app. Purple Air readings are often higher than those on Air Now.

The Purple Air site has a filter that you can apply to the map to correct the inflated numbers. In the upper-left corner of the map under the Purple Air logo, you can click on “US EPA” and apply the LRAPA filter.

The Mosquito Fire ignited near Oxbow Reservoir in Placer County on Tuesday. The blaze had reached 5,705 acres with no containment as of Wednesday night.

Amy Graff is the news editor for SFGATE. She was born and raised in the Bay Area and got her start in news at the Daily Californian newspaper at UC Berkeley where she majored in English literature. She has been with SFGATE for more than 10 years. You can email her at agraff@sfgate.com.