One hundred degrees is hot by just about any standard.

But the heat Monday wasn't just bothersome -- it was the first time in weeks and only the second time this season that temperatures in Modesto have reached 100 degrees, according to the Modesto Irrigation District.

Temperatures in Merced, Stockton and Sonora had reached 100 last week after a cooler-than-normal July.

The heat kindled concerns about fires. Health officials warned people to stay inside. Power companies, anticipating possible shortages, urged people to avoid using power as much as possible.

And relief isn't expected soon.

Temperatures are expected to soar above 100 in the Northern San Joaquin Valley throughout the rest of the week, according to the National Weather Service.

Power company officials urged customers Monday to use fans instead of air conditioners, turn on major appliances only at night or early morning and reduce lighting at home.

Following guidelines set by the California Independent System Operator, which oversees the state's power usage, utility companies also asked their industrial customers Monday to reduce computer use and keep other power-related operations to a minimum. So far, that has been done on a voluntary basis, but officials said if the statewide power supply is reduced further, they will call for "rolling black-outs" -- cutting power to certain areas at a time.

"Hopefully we'll be able to avoid those this summer," said Garith Krause, Merced Irrigation District's assistant general manager for finance and electrical services. "Though we're flirting with those."

Threat of fire high

The hot weather also brings extreme fire danger to the foothills and Sierra. Monday morning, all burn permits were suspended and open burning was banned in Tuolumne and Calaveras counties and the eastern portions of Stanislaus and San Joaquin counties.

The ban applies to all outdoor burning, expect in cities and developed campgrounds. The Stanislaus National Forest restricted campfires last week.

Capt. Ralph Selby of the California Department of Forestry and Fire Protection called it "critical fire weather."

"With the temperature and low humidity, the danger is extreme," he said.

CDF crews from this area are fighting blazes around the state, and national forest crews have also been deployed to the fires burning throughout the west.

The ban on outdoor burning will remain in effect until the weather changes and the danger lessens.

But even if fire officials can avoid problems, the danger to many folks -- especially the elderly and very young -- is health related, putting medical personnel on alert.

Pennie Rorex, spokeswoman at Emanuel Medical Center in Turlock, said they had not seen any heat-related cases Sunday or Monday, but the emergency room was prepared for the expected hot weather.

Dr. John Payne, public health officer for Stanislaus County, said as the temperature rises, so do the health risks.

The young and old are more susceptible to heat-related problems because of their inability to compensate quickly for a rise in body temperature.

Don't overdo it

Payne said two illnesses strike when hot weather arrives. Heat exhaustion is identified by flu-like symptoms -- fatigue and sweating. The other is heat stroke, with symptoms like the sudden stop of sweat, a rapid rise of body temperature or seizures.

He said it is important to wear a hat and sunscreen and drink lots of water or a sports drink. People should listen to their bodies when they start to feel overheated.

"If you feel hot and tired, get to a cool environment, rest and replenish your fluids," Payne said.

And with the expected heat wave over the next few days, people who take heed of the extreme heat need to think of their animals as well.

Jean Loveland, a veterinarian with the College Veterinarian Hospital in Modesto, said animals need plenty of water and shade when temperatures rise.

"We recommend keeping them indoors during the day if the temperature is above 95 degrees," Loveland said. "If they have to be outdoors, make sure they have plenty of shade and cool resting surfaces, since cement in direct sunlight can get extremely hot."

She said warning signs of overheating in dogs include uncontrollable panting and listlessness.

Loveland said animals should never be left alone in a car.

Bee staff writers Steve Elliott and Aaron Williams contributed to this report.

Reprinted by permission of Modesto Bee