The lights went out in office towers, shopping centers, homes and other buildings in more than a dozen Southland cities yesterday, from parts of Los Angeles' trendy Westside all the way down to communities in San Diego. Hundreds of stores and restaurants were forced to close, some people were trapped in elevators, and traffic in many areas ground to a halt as signals stopped working.

The scene was repeated in parts of Northern California, as well. In all, power officials say energy was cut to about 1.3 million customers statewide. The outages ranged from several minutes to more than two hours.

The deliberate blackouts were initiated by the California Independent System Operator, which oversees the state's power supply. Dogged for months by a shortage of electricity, the ISO's order for utilities to unilaterally cut power was reluctantly issued as energy use soared due to unseasonable warm weather—a surprising heat wave that sent temperatures in many Southern California cities soaring above 90 degrees.

Compounding the power shortage, about half of all the state's power-generating facilities were offline Monday for maintenance. Few of them are expected to begin operating again today, state officials say.

With little electricity available and the heat wave continuing for at least the next few days, experts say more blackouts are a near-certainty today and a probability for tomorrow. The last time the state threw the switch was during World War II, when lights statewide were dimmed during air-raid scares.