Air quality officials are warning that the return of high temperatures will bring smog to much of the Bay Area over the weekend.

After earlier forecasting relatively good air quality during the hot spell, the Bay Area Air Quality Management District late Friday issued a "Spare the Air" alert for Saturday, asking residents to avoid smog-producing activities such as driving or using gas-powered tools.

"Hot temperatures bring Bay Area residents outdoors, increase smog levels and unfortunately cause unhealthy air," Jack Broadbent, executive officer of the Air District, said in announcing the alert. "Consider taking transit, walking or biking to weekend destinations instead of driving so we can all enjoy cleaner air."

This is the sixth smog-related alert of the year. High ozone levels can cause problems for people with respiratory problems, and can even be irritating for those with healthy lungs.

The National Weather Service is predicting sunny and hot weather through early next week, the hottest since July, with temperatures in the low 90s in Sonoma County and upper 90s in Napa County. Cooler weather is expected by Tuesday.

The weather service warned Friday that high temperatures and low humidity will make the already perilous fire situation even worse in most areas. Hot weather "will promote critical fire weather conditions this weekend which will make for the possibility of quick spread of any fires that start," the weather service warned in a dispatch to media and emergency services managers in the area.

Air quality reports and information is available at