Marine Layer

The Southern California marine layer explained

Posted: Updated:
(Source: 3TV/CBS 5) (Source: 3TV/CBS 5)
(Source: 3TV/CBS 5) (Source: 3TV/CBS 5)
(3TV/CBS 5) -

Another escape for the DeMartino Family from the heat and this time we head to Southern California. Basically, the spot most “zonies” head to every summer.

I was blessed enough to get to work in San Diego for two years and enjoy the cool weather year-round. But one thing that always gave me trouble in my forecast was the marine layer. So, this week in my weather blog, let’s learn a little bit more about it. 

A marine layer is an air mass which develops over the surface of a large body of water such as the ocean, in the presence of a temperature inversion. The inversion itself is usually initiated by the cooling effect of the water on the surface layer of an otherwise warm air mass.

[SPECIAL SECTION: Weather blog]

As it cools, the surface air becomes denser than the warmer air above it, and thus becomes trapped below it.

The layer will also gradually increase its humidity by evaporation of the ocean, as well as by the effect of cooling itself.

So with the California coast, the offshore marine layer is typically propelled inland by a pressure gradient which develops as a result of intense heating inland, blanketing coastal communities in cooler air which, if saturated, also contains fog.

The fog lingers until the heat of the sun becomes strong enough to evaporate it, often lasting into the afternoon.

In Southern California the marine layer is most intense or persistent in May and June but can sometimes linger into July too. During these months there typically isn’t a day that does not start with a thick marine layer. Meteorologists refer to it as May Gray and June Gloom. 

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