On some rare occasions, ordinary people in the middle of an ordinary day changed the date.
In 1947, Muhammad al-Deeb, a young Bedouin shepherd searching for a lost sheep, discovered a hidden cave containing the Dead Sea Scrolls, the oldest known version of most of the Hebrew Bible. While making his rounds one night in 1972, Frank Wells, a security guard in Washington, D.C., noticed a piece of tape holding an open lock in the building where he worked—and as a result revealed the Watergate break-in, which ultimately led to the resignation of President Richard M. Nixon.
But neither has shaped so many lives so directly as Maureen Flavin, the postal worker in a remote part of Ireland's northwest coast, who helped decide the outcome of World War II in 1944, on her 21st birthday.
Her grandson, Fergus Sweeney, said she died on December 17 at a nursing home in Belmullet, Ireland, near the post office where she worked. It was 100.
The events that led Ms. Flavin to her moment of unexpected global consequences began in 1942 when she saw an advertisement for a job in the post office of the seaside village of Blacksod Point.
I got the job and learned that the remote post office also served as a weather station. Its duties included recording and transmitting weather data. She did this work diligently, even though she didn't even know where her weather reports were going.
In fact, they were part of the Allied war effort.
Ireland was neutral in World War II but quietly assisted the Allies in several ways, including by exchanging weather data with Britain. Ireland's location on the northwestern edge of Europe gave an early sense of the weather heading toward the continent. Blacksod Point was located on the westernmost point of the coast.
Weather forecasting turned out to be a key part of the most famous Allied maneuver of the war – D-Day, the invasion aimed at gaining a foothold on the European mainland.
It took two years of careful planning. American General Dwight D. decided Eisenhower, who led the attack, sent more than 160,000 troops, nearly 12,000 aircraft and nearly 7,000 naval vessels to invade a 50-mile stretch of beach along the Normandy region of the French coast.
The Allies settled on 5 June 1944, which promised a full moon, aided visibility, and low tides, allowing easy access to the beach.
A successful invasion would also depend on clear skies for the Allied air attacks and calm seas for their landings. The relatively primitive technology of the time – no satellites, no computer models – meant that the Allies would only have a few days of warning about the weather.
By 1944, Ms. Flavin's work demands had skyrocketed: she and her colleagues were now sending weather reports not every six hours, but every hour of the day.
“You won't finish one until it's time to do another,” she recalled in a 2019 documentary by Irish public broadcaster RTÉ.
On her birthday, June 3, she had a late-night shift: 12 a.m. to 4 a.m. Checking her barometer, she registered a rapid drop in pressure indicating the possibility of approaching rain or stormy weather.
The report moved from Dublin to Dunstable, the city that houses England's meteorological headquarters.
Then Ms. Flavin received an unusual series of calls about her work. A woman with an English accent asked her: “Please check. Please come back!”
I asked the postmaster's son and Blacksod Lighthouse keeper, Ted Sweeney, if she was making a mistake.
She later told Irish magazine Eye: “We checked it and rechecked it, and the numbers were the same both times, so we were happy enough.”
On the same day, General Eisenhower and his advisors were meeting at their base in England. James Stagg, a British military meteorologist, reported based on Mrs. Flavin's readings that severe weather was expected. General Eisenhower advised postponing the invasion for one day.
The general agreed. June 5 saw rough seas, strong winds, and heavy cloud cover. Some commentators – including John Ross, author of D-Day Forecast: and the Weatherman Behind Ike's Greatest Gamble (2014) – have claimed that the invasion would have failed had it occurred on that day.
Postponing the invasion beyond the sixth day raised other issues. The tides and moon were not right again for several weeks, when the Germans expected an attack. The element of surprise would have been lost. Mr. Ross told USA Today that victory in Europe may have been delayed by a year.
However, Ms. Flavin's reports indicated not only that June 5 would be disastrous, but also that the weather on June 6 would be good enough. General Eisenhower ordered the invasion and declared: “We will accept nothing less than complete victory.”
By noon on the sixth day, the sky cleared. The Allies suffered thousands of casualties, but won a European beachhead.
Joe Cattini, a British D-Day veteran, said in the RTÉ documentary: “We who invaded France on D-Day owe a great debt to Maureen of West Ireland, for without her reading from the weather we would have perished in the storms.
Maureen Flavin was born on June 3, 1923 in the village of Knockcanor in southwest Ireland, where she grew up. Her parents, Michael and Mary (Mulvihill) Flavin, ran a general store.
She married Mr. Sweeney, a lighthouse keeper, in 1946. When his mother, the postmaster, died, Mrs. Sweeney succeeded her in the job.
I first heard about the importance of its weather forecasts in 1956, when officials discussed it after the local weather station was moved from Blacksod Point to a nearby town. It gained widespread publicity during the 50th anniversary of D-Day, when meteorologist Brendan McWilliams wrote about the episode in The Irish Times.
Mr. Sweeney died in 2001. In addition to Fergus Sweeney, Mrs. Sweeney is survived by three sons, Ted, Gerry and Vincent, all of whom worked for the Irish Lighthouse Service. Daughter of Emer Schlueter. 12 other grandchildren; 20 great-grandchildren; and two great-grandchildren.
In interviews, Ms. Sweeney has marveled at the contrast between the massive powers that need weather forecasts and the small world of the Blacksod Point Post Office.
“They were out there with thousands of planes and they couldn't handle the low clouds,” she told Irish Public Radio in 2006. “We're glad we got them on the right track.” In the end, we had the last word.”