We demonstrate a direct connection between large-scale circulation patterns and surface O3 using atmospheric observations obtained during winters 2002 and 2003. Measurements at two rural sites in the northeastern U.S. revealed that median mixing ratios of O3 in winter 2003 were increased by up to 80% compared to 2002, and greatly exceeded previous spring annual maximums. To explain this we propose that strong meridional flows in winter 2003 frequently transported O3-rich mid-tropospheric air masses from high latitudes to the northeastern U.S. while cooling regional climate 4.4¿C below normal. Our measurements also show that an exceptionally elevated spring O3 maximum occurred in 2003. The impact from this winter enhancement on the levels of O3 and other species during the following months will be largely driven by actual climatic conditions.