Early summer weather is prompting the state’s firefighting agency to declare the opening of fire season in 19 California counties. The declaration will be made Monday for counties spreading from Nevada County in the north to San Diego County in the south. June 12 will be the opening of fire season for other counties in the north. Separately, Orange County’s fire authority said it will declare the season on Wednesday. The CDF declaration means that the agency will increase its fire preparedness. The could include hiring seasonal firefighters, staffing some fire stations around the clock and moving firefighting planes from Sacramento to areas around the state that have a high fire danger.