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Abstract Previous studies have suggested that variability in the Gulf Stream (GS) region can lead North Atlantic atmospheric variability. However, it remains unclear what GS characteristic is most important in driving this lead time. Here, we show that the GS sensible heat flux (SHF) gradient specifically leads the North Atlantic Oscillation (NAO) by 1 month. This lag relationship occurs only when climatological sea‐surface temperature and SHF gradients are largest in late winter. Further analysis reveals that fine‐scale gradients (∼50 km) are critical. A month prior to a negative NAO, stronger than normal diabatic frontogenesis associated with anomalously strong SHF gradients is observed over the separated GS region. This is collocated with a North Atlantic eddy‐driven jet located in its Southern regime. These results suggest that knowledge of fine‐scale air‐sea heat flux gradients in late winter can potentially provide useful information about the NAO in weather forecasts and climate prediction systems.