Jessica Roy | Los Angeles Times (TNS) Rising temperatures are pushing California’s power grid to its limit — again. Forecasters say extreme heat will bake the state this week, starting what is expected to be the longest heat wave of the year. Northern California, the Central Valley and the southwestern deserts in particular are bracing for dangerous temperatures through the extended Fourth of July holiday weekend and into early next week. The demand for around-the-clock cooling could strain the state’s utilities, and the increased risk of wildfires also threatens to force some precautionary power cutoffs.