Thunderstorm Gains Place in History Book : Weather: Early morning rain appears to be the first ever measured here on July 16 since records began being kept in 1855.

While part of the nation suffered under a killer heat wave, a freak summer thunderstorm rattled through Orange County early Sunday like some strange winter flashback, bringing on-and-off rain, power outages and spoiled weekend plans.

It may have been the first rain here on a July 16 since local weather records started being kept in 1855.

Lightning knocked out power to 15,000 Southern California Edison customers between 3 and 3:30 a.m. but was restored so quickly that, for the most part, customers with digital clocks in need of resetting were only the ones who noticed.

“We had several momentary outages and one circuit break for about a half-hour,” said Millie Paul, spokeswoman for Edison, adding that customers were affected in Santa Ana, Villa Park, Huntington Beach, Seal Beach, Garden Grove, Tustin and Orange.

The sporadic showers, although sometimes intense, dumped tiny amounts of rain in the county--.15 was reported in Tustin and .08 at El Toro, for example--but managed to dampen attendance at some area events and amusement parks, at least until the sun broke through in mid-afternoon.

By noon, when temperatures had reached into the muggy 80s, fewer than 10,000 had passed through the turnstiles at the Orange County Fair, spokeswoman Lynn Schultz said.

But the rain had almost no impact at Disneyland, although the Mad Tea Party ride did not open right away.

“We are absolutely consistent with where we were last Sunday,” Disneyland spokesman John McClintock said. “We did open a little more slowly.”

Apart from the brief power outages and the temporary inconvenience to organizers and participants of summer events, the storm caused little other damage. The California Highway Patrol reported no accidents attributable to the rain by midday.

The weather, while unusual, was in stark contrast to the triple-digit temperatures that have baked the Midwest for a week, causing more than 100 deaths, mostly in the Chicago area.

Curiously, rain on July 16 is such a climatological rarity that not even the records of Jim Sleeper, Orange County’s official chronicler of historical oddities, show any rainfall for the date going back to 1855--when someone first began keeping track.

“This was really quite a surprise,” said Nola Sleeper, wife of the Orange County historian. Going through her husband’s records, she said, “There is no rain at all for this date. Around here, July has always been the driest month.”

In the official language of weather, the strange storm and rain were the result of “an upper level disturbance with convective showers,” said Curtis Brack, a meteorologist with WeatherData Inc., which provides forecast information for The Times.

The weather pattern is normal for July and August over parts of the Southwest, especially the desert, Brack said, when a high pressure system pulls a “monsoonal” flow of moisture up from Northern Baja California and the Pacific Ocean, dumping it in the desert and Arizona.

This time, the system “just drifted westward,” Brack said. “This is fairly unusual.”

Brack said the weather pattern might hang on through Tuesday, with a slight chance of more showers, including thundershowers in the afternoon and evening.