Dry summers—they’re one of the perks of living in Los Angeles. Ninety-two percent of precipitation falls between the months of November and April. But while it’s rare, summer rain does sometimes dampen L.A.’s summertime fun, forcing Angelenos to fumble through their closets in search of an umbrella.
Aside from marine layer drizzle, the main source of warm season rain is monsoonal moisture leaking from the interior deserts onto the coastal plain. Thunder and lightning often accompany the rainfall. The downtown Los Angeles weather station recorded its one-day rainfall record for the month of July on July 14, 1886, when 0.24 inches fell. August typically brings more monsoonal rain than July; that month’s record is 2.06 inches on August 17, 1977.
Another, even rarer source of summer rain is a tropical storm. The remnant of one came ashore on September 25, 1939, dumping 5.62 inches of rain on downtown Los Angeles. (I wrote about this storm—and an 1862 hurricane—a couple years ago at KCET.) And even when storms don’t impact the region directly, their residual moisture can bring unseasonable rainfall.
Source: “Climate of Los Angeles,” NOAA Technical Memorandum NWS WR-261.
Related: A Snowstorm in Los Angeles? It’s Happened. (City Think blog, Los Angeles Magazine)