Coastal California has seen less fog and more humidity due to El Niño
By CBS Bay Area
Fogust? Where are you?
Normally, in the Bay Area, the month of August is referred to as Fogust because of how thick the marine layer usually is this time of year, especially along the coast. But this year, have you noticed a lot more sunshine? This week we’ll zoom into the reason why summer this year hasn’t been as foggy as normal.
It all revolves around El Niño and warmer water temperatures. Not only are sea surface temperatures above average at the equatorial Pacific, which is a sign of El Niño, but the warm water also extends especially next to southern California and goes all the way up the West Coast.
Even over the Pacific Northwest, coastal waters are warmer; this is normally where the cooler water from the California Current travels south down the coast. El Niño disrupts weather patterns; the typical Pacific high pressure that spins clockwise brings northwesterly winds along the coast is not there.
And it’s the cool water from the California Current and upwelling that allows our dense coastal fog to form. The ocean water is cooler than the air above it, and lowers the air temperature down to the dew point, which creates fog. But when the water isn’t cool enough, it won’t cool down the air enough to get it to the dew point, so fog won’t form.
The warmer water increases the rate of evaporation at the surface, which in turn increases dew points on land. A combination of the warm sea surface temperatures and monsoonal moisture is the reason many places across coastal California are dealing with record levels of summertime humidity. San Francisco hasn’t been this humid since 2014, at the 10th highest on record, and records go back to 1932. Santa Barbara is feeling the 4th most humid, with records dating back to 1937, and Los Angeles the 8th most humid, with records since 1931.
Higher dew points have also led to some record-warm summer nights. The average low temperature is at the 8th highest for Los Angeles, 6th highest for Santa Barbara, and 7th highest for San Francisco. This is because water vapor in the air, whether or not in the form of fog, acts like a blanket on the atmosphere, trapping in heat and not allowing low temperatures to drop as much.
So, it’s the warmer water brought by El Niño that’s not allowing as much fog to form, but still bringing record levels of humidity and warm summer nights.
