Now that we are at the 75th anniversary to the day, the importance of Stagg's met forecast (with due acknowledgement to his team, langleybaston!) seems more key to its success than ever. If he hadn't prevailed (his US opposites disagreed) D-Day would have been a wipeout. If he hadn't persuaded Eisenhower that the following day provided a brief but only just acceptable opportunity to go then the actual wx for the remaining possibilities in June meant that the 6th was the one and only chance to invade. What would have happened without D-Day? A Europe under the Red Army to the Atlantic Coast? Who knows, but the accuracy of that forecast was key to liberating the democracies of Western Europe.
Interestingly, Stagg's forecast that day excluded the observations from occupied France, normally available thanks to Ultra. The Germans had changed codes...
https://www.metoffice.gov.uk/binarie...compressed.pdf