Smoke in Bay Area leads to Spare the Air alert's extension

Wildfire smoke continues to linger above the Bay Area, defying forecasts and prompting authorities to extend the Spare the Air alert again.

The Spare the Air alert is in effect through Saturday, the Bay Area Air Quality Management District said Friday. 

Air quality was considered to be unhealthy for sensitive groups from Santa Rosa to San Jose around midday Friday. 

The National Weather Service expects conditions to improve tomorrow.

"Hate the smoke? We have some exciting news for you," the NWS tweeted. "Smoke will gradually improve today, then greatly improve by late Saturday as a potent upper low approaches"

The National Weather Service had said earlier in the week that shifting winds would push out the smoke, which originated with wildfires in Northern California and Oregon, by late Thursday or Friday.