August 23, 2019 - Cloud bank along Southern California coast

Sweltering temperatures and onshore breezes brought a heavy blanket of fog across much of Southern California in mid-August 2019. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a true-color image of the cloudy scene on August 15.

A large bank of marine stratocumulus clouds stretches for hundreds of miles over the Pacific Ocean. As the bank approaches the coast of California the texture appears much finer than the layer over the ocean, a clue that the layer has lowered closer to the ground, creating “low cloud”, or fog. Swirls in the clouds are created by breezes just off the coast and over the warm land.

Temperatures across much of Southern California registered well into the 90s, in some places reaching more than 100°F (37.8°C) in mid-August. Marine clouds develop well offshore, triggered by moisture over cold ocean water. When a contrast in temperature occurs—when inland air is hot and the air over the ocean is cooler—it is likely that the result will be that the marine layer will be drawn inland with strong onshore breezes. The larger the temperature contrast, the stronger is the trend to pull the marine layer onshore, which is why heat waves inland often bring heavy fog along the coast of California.

Image Facts
Satellite: Terra
Date Acquired: 8/15/2019
Resolutions: 1km (272.2 KB), 500m (743.7 KB), 250m (594.8 KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC