The sun did not shine on many Southern California cities for much of May

The extra sun this weekend has been a welcome sight for many in SoCal who have been under clouds for much of May.

If you thought we saw many more cloudy days than sunny days, you’re absolutely right.

what you need to know

  • Marine layer clouds are common throughout central and southern California in May and June.
  • People who live in SoCal often refer to it as “May Grey” and “June Gloom.”
  • Most marine layers form where warm air is forced over cold ocean currents.
  • The marine layer can be as shallow as 100 feet or as deep as 5,000 feet.

Marine layer clouds were slow to clear or barely cleared in May for many cities west of the mountains.

Below I’m summarizing how many sunny, partly cloudy, and overcast days we saw in SoCal.

There is a science behind the marine layer

This cloudy weather pattern commonly occurs in late spring and early summer, along the west coast of the continents due to cooler water running along their shorelines.

California is influenced by the cold California Current that comes from the Gulf of Alaska.

A shallow layer of air, also known as the marine layer, forms when warmer, more humid air passes over a body of cold water and then cools and condenses into clouds that we see forming offshore every afternoon.

In the image below, you can see the cloud cover of the marine layer extending from the coast of Baja California to the coast of British Columbia.


In late spring and early summer, the land begins to warm at a much faster rate than the ocean.

The uneven heating rates of land and water create the wind that carries those clouds over land, sometimes up to 80 miles inland or more!

A deeper marine layer generally results in extensive cloud cover extending inland, often as far as the foothills of mountains.

Clouds in the marine layer can look and act differently from year to year.

The depth of the sea layer and the length of time that sea layer clouds remain during the day and during the months of May and June depend on large-scale weather patterns passing at high altitudes.

If low pressure systems are present as we saw in May, that creates the westerly flow that drives the clouds towards the coast and sometimes further inland than just the coast.

Low pressure systems also thicken clouds, causing drizzle and sometimes light rain.

High pressure systems, on the other hand, bring sinking air over the region that can crush marine layer clouds to the land surface.

If the force of the downward air is very strong, the clouds can remain confined to the beaches while the sun shines on the basins and valleys.

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