noun - June Gloom is a Southern California term for a weather pattern that results in cloudy, overcast skies with cool temperatures during the late spring and early summer, particularly in the month of June. June Gloom in Southern California is caused by the marine layer effect common to the West Coast of America, and is enhanced by the Catalina eddy local to Southern California. The phenomenon can be disorienting and disappointing to visitors from inland areas who, coming from the summer heat, do not expect cool temperatures, clouds and fog along the coast.
May and June together are usually the cloudiest months in coastal Southern California. June Gloom has other colloquial names if the same weather pattern occurs in May (May gray) if it begins early, July (No-sky July) or August (Fogust) if it continues past June.
June Gloom is stronger in years associated with a La Niña, and weaker or nonexistent in years with an El Niño. This weather pattern occurs in other parts of the world where climates and conditions are similar. Scientists study the cloud fields that make up June Gloom to increase understanding of cloud behavior at the onset of drizzle and precipitation.
The condition is prevalent in many parts of the world where an offshore marine layer of stratus or stratocumulus clouds is common, such as the western coasts of continents including Peru, Namibia, Western Australia, Atlantic Sahara and Northern California, particularly San Francisco.
A typical June Gloom day consists of marine stratus clouds covering the coast of southern California, extending a varying distance inland depending on the strength of the June Gloom effect each day. The fog and clouds, which are formed by the marine layer, move in at night, usually after midnight, and typically dissipate in the late morning, giving way to clear, sunny skies. During a heavy June Gloom season, the condition may persist into the afternoon, or even all day during an exceptionally strong event.
If the air is saturated with moisture, fog also may develop with June Gloom. Early mornings during June Gloom are typically foggy, with frequent light mist and occasional drizzle. Fog and drizzle normally are found near the furthest inland extent of the gloom, where the cloud deck is closest to the ground. The fog recedes and reveals low clouds by mid-to-late morning; by late morning to early afternoon, solar heating usually is sufficient to evaporate the clouds altogether.
The phenomenon forms earliest and lasts longest at the coast, with later formation and earlier dissipation in areas 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 on exceptionally strong June Gloom mornings. 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.
May and June
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.