Severe thunderstorms roared into the Phoenix area late Tuesday afternoon, drenching some parts of the Valley and creating dangerous conditions for evening commuters. So much rainfall had fallen in a short span of time — up to 2 inches in one hour in central Phoenix — that the National Weather Service was referring to the storm as a 100-year event, meaning that amount of rainfall has a 1 percent chance of happening in any given year, in a specific location. Authorities urged Valley residents to avoid driving during the storm, as the rainfall had created headaches for motorists on freeways and surface streets.