Standard&Poor's Ratings Services has assigned its 'AA-' rating to Seattle, Wash.'s municipal light and power improvement and refunding revenue bonds, series 2011A; and improvement revenue bonds, series 2011B. At the same time, Standard&Poor's affirmed its 'AA-' rating on the system's (doing business as Seattle City Light [SCL]) parity lien debt and its 'AA-' underlying rating on the debt. The outlook is stable. The 2011B bonds will be sold as New Clean Renewable Energy Bonds (CREBs). The rating reflects our opinion of the following strengths: A low-cost hydro-based generation portfolio that can meet demand under most water conditions ; A strong and diverse customer base; Good financial management; and Competitive retail rates, even after accounting for sizable