early afternoon, solar heating usually is sufficient to evaporate the clouds, and the sun emerges. The phenomenon forms earliest and lasts longest at the coast, with weaker effects as it moves further inland. When the marine layer is strong and deep, clouds can fill the Los Angeles Basin and spill over into the San Fernando Valley and San Gabriel Valley, even extending into the Santa Clarita Valley and Inland Empire on exceptionally strong June Gloom mornings. If conditions are not as strong, the Basin may be filled while the valleys may be clear. It is not uncommon for motorists to drive over the Sepulveda Pass from the clear, sunny San Fernando Valley and plunge into a cloudy, fog-filled Los Angeles. On a weak June Gloom morning, the clouds and fog may only be present within a mile or two of the coastline, affecting only the beach cities. Climate effects A combination of atmospheric and oceanic conditions must be just right in order for June Gloom to form, and these conditions usually align only around May and June of each year. These include the marine layer effect common to the West Coast of the United States, an atmospheric inversion caused by subsidence of high-pressure air from the subtropical ridge, and sufficiently cool ocean water off the coast. The June Gloom pattern is also enhanced by the Catalina eddy local to southern California. The months of May and June are typically the cloudiest months of the year in coastal southern California, having only 59% and 58% sunny days, respectively, on average in San Diego. The number of days in May and June that are "gloomy" vary from year to year. Anomalies in sea surface temperature can be used to forecast the length and intensity of the June Gloom phenomenon in a given season. Years with warmer ocean temperatures, referred to as El Niño, may result in fewer gray days in May and June. Cooler ocean temperatures, associated with La Niña, usually foretell a more gray period. The climate charts below show a clear drop in the mean monthly sunshine hours and percent possible sunshine for the months of May and June, which are the two months when the June Gloom pattern is the strongest. June Gloom has been reported by some Californians to bring on symptoms consistent with seasonal affective disorder, although this is not well-supported by evidence. However, the normally-very-sunny Los