Temperatures throughout the Central Valley soared well over the 100-degree mark Tuesday, and forecasters say there's a threat the same will happen today. High points in the Northern San Joaquin Valley were Sonora at 106 and Stockton at 105, matching Fresno and Bakersfield.

The National Weather Service reported 104 for Merced, with Turlock topping out at 103 and Modesto at 101.

Today's highs could hit 107 in some parts of the valley, forecasters said.

Aggravating the misery of sweltering heat, Northern San Joaquin Valley air quality is expected to fall in the unhealthy range today for the fifth day in a row.

Pollution levels have led the San Joaquin Valley Air Pollution Control District to declare today a Spare the Air day. Under the Spare the Air program, valley residents are asked to reduce car trips, postpone yard work using gas-powered equipment, limit barbecuing and avoid using motorboats and off-road vehicles.

Soaring temperatures and continued poor air quality also have taxed community health resources, although health-care workers in Modesto and Turlock reported no cases of heat-related illness Tuesday.

"Most everybody's being smart, and they're staying out of the heat," said Dr. Gene La Monica, director of the Stanislaus County Health Services Urgent Care Center.

Signs of heat exhaustion include headaches, thirst, fatigue and fever. The more severe heat stroke will cause vomiting, headaches and confusion.

Dr. Robert Craig of Turlock's Emmanuel Medical Center advised anyone suffering from heat-related illness to lie down in a cool place and consider calling a doctor or making a trip to an emergency room if there is no improvement or if mental confusion occurs.

Health authorities also warned that the high level of air pollution as well as the heat should keep those most vulnerable -- children, the elderly and pregnant women -- inside. Healthy adults who work outside may also face health problems if they engage in vigorous activity for more than six hours, health officials said.

For those who must work outside, health-care workers advise drinking plenty of water -- at least twice the normal amount.

National Weather Service forecasters are offering the possibility of some relief toward the end of the week for residents of the northern San Joaquin Valley.

Temperatures for Thursday through Saturday should dip to 97 or 98. And Sunday? Forecasters are calling for highs of 85 to 90 degrees.

Lows tonight will dip to near 70. Lows for Thursday through Saturday night should be about 10 degrees cooler.

Bee staff writers Kerry McCray and Ellen Chrismer contributed to this report.

Reprinted by permission of Modesto Bee