The D-Day Landings were delayed by two days after a report from Ireland predicted bad weather.
Maureen Sweeney forecasted a storm coming from the Atlantic Ocean in June 1944, while working in the Blacksod Lighthouse in Co Mayo.
Knockanure-born Maureen Sweeney, whose maiden name was Flavin, was 21-years-old when she forecast an impending storm from the weather station.
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Her forecast delayed the timing of the D-Day landings and helped secure victory for the Allies.
World War Two veterans have gathered in Normandy today to mark the 80th anniversary of the D-Day landings.
Ms Sweeney's son, Ted, says she didn't realise the significance of her forecast at the time:
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