San Diego May Gray and June Gloom
Overhead in the San Diego Zoo parking lot the other day: "I thought Southern California was all sun." All sun unless it is May or June! You roll the dice if you visit during these months. While we started and nearly completed May with mostly cloudy, dreary weather, we are back to getting afternoon sunshine. May Gray and June Gloom usually follow the pattern of mostly dreary til afternoon and the sunny. The coastal areas are 'iffy' on that formula, at best. How June Gloom Forms
READ ON: Fog comes in on little cat feet -- and a bit of warm air
ARTICLE FROM THE UNION-TRIBUNE--May 18, 2007
Fog is simply water droplets suspended in the air at the Earth's surface.
It forms in a variety of ways, but most of the fog seen at the coast is created when relatively warm, moist air moves over the cool Pacific. After contact with the water -- which is in the 50s or low 60s most months of the year -- moisture in the air cools, condenses and becomes visible as fog. (It's considered "dense" when visibility is reduced to a quarter-mile or less.)
In late spring, fog formed off the coast often ventures onshore because of inland conditions. Extreme heating of the desert floor causes the air above it to rise, which creates low atmospheric pressure. That low pressure acts like a magnet to cooler air over the coastal waters.
If fog is present in the air pulled inland, it will often coat Point Loma, which juts into the Pacific.
As summer wears on, ocean temperatures off the Southern California coast increase to about 70 degrees, and fog is less likely to form.
Fog can return in winter, when coastal waters have cooled again, but different forces are at work. In winter, warm air pushed ahead of rain-producing cold fronts crosses the cool waters, condensation occurs and fog forms.
And then it is spring again.
-- Robert Krier
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