A mere five days ago, San Francisco broke a record for rainfall on that date—a notable occurrence after a dry water year. Bookending a relatively warm and overall pleasant week, we now have the first Spare the Air Day of the season as a dome of high pressure sits atop the Bay Area.
It hasn’t been particularly foggy this spring, but it’s about to get smoggy as ozone levels and atmospheric particulate matter increase to unhealthy levels, according to the National Weather Service. Whenever the Air Quality Index (AQI) exceeds 100 in any region overseen by the Bay Area Air Quality Management district, the agency issues an alert.
While San Francisco is likely to see ozone levels peak well below that threshold as temperatures climb into the low 80s, much of Wine Country and parts of the East Bay are likely to see temperatures and the AQI climb well above 100. In some places, low temperatures tonight may only fall into the 70s.
Consequently, older adults and young children are encouraged to stay indoors. If you’re planning to exercise outdoors today, you probably should have woken up for an early jog.
A Spare the Air alert isn’t purely a meteorological phenomenon, either. Increased vehicular traffic is also to blame for smog. Warm, windless weather and the region’s topography combine with car exhaust to generate ozone that cannot disperse—and evidence strongly suggests that, in spite of the rise of hybrid work, traffic on the region’s freeways has nearly reached pre-pandemic levels.
As of Friday morning, PG&E had not issued any warnings beyond a recommendation to set the thermostat to 70, keep the fridge door closed and rely on ceiling fans as much as possible. But state officials have intimated that excessive heat this summer could exacerbate the fire danger from a dry winter, spurring the beleaguered utility to implement rolling blackouts.
Temperatures are expected to cool significantly by Sunday, with San Francisco’s temperatures topping out in the mid-60s and areas of Mendocino likely to see small amounts of rain.Peter-Astrid Kane can be reached at [email protected].