Smog Day Afternoon : Weather: Continued summer-like temperatures are expected to bring the Southland its first Stage 1 air quality alert of the season today.

Temperatures and smog levels soared to summer levels again on Monday, sending Southern Californians scurrying for air-conditioned buildings and the beach.

With the area lacking the protection of a thick layer of cool, moist marine air, temperatures reached 97 degrees in Woodland Hills, 96 in Monrovia and 93 in Van Nuys by midafternoon Monday, nine days before the official start of summer, the National Weather Service reported. In Downtown Los Angeles, the mercury hit 90.

It was the third straight day of a mini-heat wave that drove Angelenos indoors or to the seashore for relief. On Sunday, the temperature peaked at 101 in Woodland Hills.

The hot weather was accompanied by worsened pollution, especially in the valleys and the Inland Empire, where thick smog shielded the mountains from view on Monday. Officials said air quality in the east San Bernardino Valley was unhealthful. In Los Angeles, pollution was moderate.

Despite slightly lower temperatures forecast for today, the South Coast Air Quality Management District said Stage 1 smog alerts--the first of the season--would be in effect today for parts of the San Gabriel Valley, where pollution in the Los Angeles Basin is often heaviest. Any vigorous outdoor activity is unwise during Stage 1 alerts.

Conditions are expected to be unhealthful in the central city and the Santa Clarita Valley. The San Fernando Valley can expect moderate air quality, the AQMD said.

In Woodland Hills, Monday’s one-two punch of sweltering heat and deteriorating air quality produced “watery eyes and the normal nosebleeds” for a handful of students at Calabash Street School, said Principal Loretta Norwalt. Other children skipped handball and the swings in favor of quiet, shady spots during recess and lunch.

“Six of our rooms have air conditioning, so that helps a lot,” Norwalt said. But three of the school’s classrooms rely only on open windows for ventilation, including one first-grade classroom where only 12 of 30 students showed up Monday.

Meteorologist Steve Maneikis of WeatherData Inc., which provides forecasts for The Times, said the brief hot spell has been precipitated by a stubborn high-pressure ridge hovering over Southern California.

“With that keeping the marine layer very thin and confined to the coast, it’s allowing you to heat up quicker early in the day, without the low clouds and early-morning fog,” Maneikis said. “Once the marine layer starts to return, which is what it looks like it’ll start to be doing here, you’re not going to be warming up so much.”

Maneikis forecast more sunny skies for today, but said temperatures may cool slightly, especially along the coast.