A Few Drops Set a Rainfall Record for the Date : Weather: Unstable weather brought thunder, lightning and a very, very brief shower that nevertheless is one for the books.

When four-hundredths of an inch of rain (can you hear them laughing in Seattle?) fell in San Diego on Monday, weathermen reached for the record books.

It was the most rain recorded on June 22 since record-keeping began in 1850, said Wilbur Shigehara, chief forecaster for the National Weather Service in San Diego.

In Imperial Beach, officials reported .02 inches of rain during eight minutes of showers Monday morning, Shigehara said.

“To put the record amount of rainfall in perspective, we normally receive six-hundredths of an inch of rain in all of June,” Shigehara said.

The sudden thundershower snarled traffic on county freeways. Accidents backed up traffic on Interstate 5, Interstate 8, California 94 and California 163 in the morning, said Timothy McLaughlin, a spokesman for the California Highway Patrol. No one was seriously injured, McLaughlin said.

Thick clouds hovered over San Diego the rest of the day. But the cloudy skies were not the usual “June gloom” weather pattern, Shigehara said.

An unusual flow of moist air from the south brought the clouds and rain into San Diego. Two competing pressure systems surrounding San Diego are forcing the moist air into the region, he said. When high and low pressure systems meet, unstable air is created, which in turn can cause thunder.

Monday’s rainfall came just before the end of the rainy season June 30, Shigehara said. So far this season, San Diego has received nearly 13 inches of rain. Normally the area receives an average of 9.32 inches of rain, he said.

Moist, southerly winds will continue at least through today, Shigehara said. A drying pattern is expected to begin by Wednesday.

The weather service predicted partly cloudy skies for today and a 20% chance of showers or thunderstorms.

The coastal strip is expected to reach a high between 62 and 72 degrees today. The low will be about 60 degrees, Shigehara said.

The inland areas should reach about 85 degrees with a low in the upper 50s, Shigehara said.

Temperatures in the mountains should climb to 78 degrees and fall to 50 degrees at night.

The deserts should have a high temperature in the low 100s today, and a low temperature in the 60s, Shigehara said.