It took until the end of June, but thermometers in Modesto and the surrounding area finally hit triple digits Tuesday.

Modesto, 100. Turlock, 103. Merced, 103. Los Banos, 104. Stockton, 105.

It was even hot in the foothills and the Sierra. Sonora, 103. Mariposa, 98. Yosemite, 92.

Don't turn off the air condi- tioning or put away the sunscreen. Forecasters predict more hot weather today and Thursday, but it should cool down some going into the holiday weekend.

Combine the hot weather, low humidity, bone-dry foothills and Fourth of July fireworks and you have a recipe for fire -- big fires.

At campgrounds, fireworks are first and foremost on the list of potential fire causes this weekend, said Richard Imlach, a California Department of Forestry battalion chief. "We absolutely do not allow fireworks, not safe and sane or illegal fireworks."

He warned of campfires, too. Most campgrounds allow fires in designated areas. However, at the height of summer, rules can change, Stanislaus County Fire Warden Russ Richards warned.

The hot weather prompts health concerns, too. The same advice holds every year: wear sunscreen, drink lots of water, stay out of the sun and avoid strenuous outdoor activities.

Ignoring those tips raises your chance of suffering from heat stress or stroke, said Dr. Alvaro Garza, Stanislaus County's public health officer.

The heat isn't the only problem. Today is the first "Spare the Air Day" of the summer because unhealthy air quality is forecast.

The San Joaquin Valley Air Pollution Control District issued the following health advisory: Sensitive children and adults should curtail outdoor activities, and everyone else should limit prolonged outdoor exertion during peak ozone periods.

On Spare the Air Days, residents are asked to carpool, avoid using lawnmowers or any device with a two-stroke engine (like most personal watercraft), and avoid using solvents and lighter fluids.

Today is the first Spare the Air Day in the Northern San Joaquin Valley. The Bee will alert readers to Spare the Air Days in the right-hand column of The Weather Page at the back of the B section.

Bee staff writer Steve Elliott contributed to this report.

Reprinted by permission of Modesto Bee.