California entered 2017 hoping a wet winter could end the state’s six-year drought. Be careful what you wish for. Northern California and the San Joaquin Valley are bracing for potential flooding this weekend, as a massive weather system known as an atmospheric river builds off the coast. Forecasters say that by Monday, rainfall and river flows could reach totals not seen in more than a decade. Already, some regions north of Sacramento are issuing voluntary evacuation orders and several northern counties, including Sacramento, are readying sandbag stations.