La Niña, a phenomenon marked by the cooling of water in the equatorial Pacific, is a major driving force behind weather around the globe. Just last month, the forecast was neutral, which meant chances of Los Angeles getting its average of 15 inches of precipitation looked good. But the new report points to a 70 percent chance of La Niña development in the fall, sloping to 55 percent in the winter. That might mean a drier, warmer winter in the southern tier of the U.S., which doesn’t bode well for SoCal as it enters its sixth year of drought.