FOLSOM -- The weather across California has been heating up for several days now, causing concern for the operators of the state power grid.

The managers of the state power supply and Pacific Gas and Electric Co. have declared Thursday a "Flex Your Power Now!" day and asked California residents to reduce their power usage, especially in the afternoon.

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Today is the fourth day of this summer's first major heat wave, placing a high demand on California's energy system, according to the California Independent System Operator (ISO), which monitors the power grid.

Peak demand is forecast for 4 p.m., when energy use is expected to reach 46,182 megawatts. The previous record was 45,597 megawatts on Sept. 8.

Friday is also predicted to be a record-breaking day with peak demand forecast at 46,573 megawatts, according to the ISO.

The ISO predicted that enough power would be available to meet the expected demand but warned of little leeway if an emergency were to occur. If a power plant or transmission line were to go down, the ISO warned that such an event could cause blackouts and brownouts.

"The summer energy outlook looks good for California, but on hot days we need to remain vigilant," PG&E spokesman Paul Moreno said today. "We don't anticipate problems but we're never completely out of the woods."

Moreno recommended that residents set thermostats at 78 degrees or higher, and put off the use of major appliances until after 7 p.m. According to Moreno, the highest energy demand occurs between 2 p.m. and 7 p.m. because it is the hottest portion of the day and the time that residents come home from work and begin preparing dinner or doing chores that demand power.

PG&E customers are asked to use a fan instead of air conditioning, draw the drapes on the sunny side of a home and turn off unnecessary lights and appliances in order to conserve power. Major appliances that residents should wait until 7 p.m. to use include pool pumps, dishwashers, clothes dryers and air conditioners.

Compact fluorescent light bulbs are also recommended over traditional incandescent bulbs because fluorescent bulbs use a quarter of the energy and last six times longer, according to Moreno.

PG&E is also offering a new incentive to customers to use less energy. Those who use 20 percent less energy this summer than last summer will be rewarded with an additional 20 percent discount on their energy bills, according to Moreno.

Residents can learn more about how to save energy at the Flex Your Power Web site.