Year to Year Variability of Marine Layer Clouds at San Diego

As most long-time residents of coastal Southern California areas know, the amount of marine layer cloudiness varies greatly from year to year. The amount of cloudiness in a given year is controlled by many factors including large-scale high and low pressure systems, local winds, and sea surface temperatures. During July 2010 all of these factors played a role in making this the cloudiest July in the last 50 years here in San Diego.

Cloudiness observations at San Diego Lindbergh Field provide a way to look at how marine layer clouds have varied over the last 50 years. Lindbergh Field is located next to San Diego Bay and should be indicative of local coastal conditions. The plots below only include clouds that had a cloud base lower than 2500 ft in order to focus on low Marine Layer clouds.

The four plots below show cloudiness (fraction of time cloud present during daylight hours) for the months of May, June, July, and August which are the primary months of marine layer cloud formation. Each graph shows the monthly average cloudiness from 1960 to 2013. The red line on each plot indicates the long-term monthly mean cloudiness over the 54 year period.

The plots show that there is quite a bit of variability from year to year. Both June and July of 2010 had much more marine layer clouds than normal, with July having the most ever over the last 50+ years.

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