The decision to change strategy is sometimes claimed as a major mistake by the Oberkommando der Luftwaffe (OKL). It is argued that persisting with attacks on RAF airfields might have won air superiority for the Luftwaffe. Others argue that the Luftwaffe made little impression on Fighter Command in the last week of August and first week of September and that the shift in strategy was not decisive. It has also been argued that it was doubtful the Luftwaffe could have won air superiority before the "weather window" began to deteriorate in October. It was also possible, if RAF losses became severe, that they could pull out to the north, wait for the German invasion, then redeploy southward again. Other historians argue that the outcome of the air battle was irrelevant; the massive numerical superiority of British naval forces and the inherent weakness of the Kriegsmarine would have made the projected German invasion, Unternehmen Seelöwe (Operation Sea Lion), a disaster with or without German air superiority.
What month would the weather window begin to decline?
October