Fire season has been getting longer in Silicon Valley, and with it are smoke and air quality issues. The Bay Area is full of micro climates, and that translates to areas which are more or less impacted by these problems.
- windier areas, where the breeze blows from the San Francisco Bay or the Monterey Bay to inland areas may have the cleanest air if the fires generating the smoke are far away
- lower elevation areas may have less smoke if the blazes causing the smoke are far (distant fires seem to cause the smoke to be higher up)
Weather patterns, smoke and air quality
Please note, I’m not a meteorologist, but am going to share my observations from living here most of my life (except a few years from 18-23, I’ve been in this area).
Our Silicon Valley weather is dominated by the nearby Pacific Ocean. Most of the time, the coast enjoys foggy mornings and sunnier afternoons, and the inland areas are impacted by that. When the coastal overcast burns off, clouds recede from the Monterey Bay. In the mid to late afternoon, winds reverse, and breezes pick up. This is also true with winds coming off the San Francisco Bay and moving south along the Calaveras Mountains.
Wind patterns are key for the discussion around smoke and air quality.
Most of Silicon Valley is in the Santa Clara Valley. Valleys can trap air in what is called a heat inversion at times (a warm area prevents the air below it from moving around – we see this in winter sometimes). When that happens, we get a “Spare the Air” day and are asked to do what we can to help the air pollution problem. The coastal areas don’t have this issue, so usually don’t have smog. They have plenty of wind from the ocean. If there is a fire elsewhere in California, most of the time it does not impact the coast to the same degree as the inland areas.
As a general rule, when the fog is pushed in from the Pacific, it comes through any low points or passes it can find. The foggier areas to the north of Silicon Valley, such as Daly City and San Francisco, don’t offer much resistance to the push from the Pacific. Nearly always, coastal wind means cleaner air. (more…)