SAN FRANCISCO (CBS SF) — Northern California residents awaited the arrival Wednesday of a high pressure system from the Pacific Ocean that was forecast to send temperatures soaring and drape a layer of unhealthy smog over the Bay Area.

The Bay Area Air Quality Management District issued a Spare the Air Alert for smog beginning on Thursday.

“A high-pressure system is moving into the Bay Area, causing light winds and high temperatures inland,” air quality officials said. “In combination with motor vehicle exhaust, these conditions will lead to elevated concentrations of ozone, or smog.”

Spare the Air Alerts are issued when ozone pollution is forecast to reach unhealthy levels. Ozone can cause throat irritation, congestion, chest pain, trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema.

“Another period of hot weather is a reminder that we need to reduce our daily driving to reduce air pollution,” said Jack Broadbent, executive officer of the Air District. “Sharing rides, taking transit, biking and walking can help make the air cleaner and healthier in the Bay Area.”

The National Weather Service predicted that temperatures would soar into triple digits in some inland areas by Friday.

“We’re looking at highs around 100 in the Concord and Livermore area,” Drew Peterson, a forecaster with the National Weather Service, told the San Francisco Chronicle.