CORPUS CHRISTI, Texas — You might know that weather played an important role in the execution of Operation Overlord: the Invasion of Normandy, known as D-Day.
The invasion was the largest amphibious invasion in military history, including land, air, and sea forces of the allied armies. It's known as a key turning point in World War II. However, June 6, 1944 was not the original date chosen for the attack. June 5, 1944 was the original date for D-Day as military meteorologists were forecasting low tides, a full moon, and fair weather, although, Allied Forces' meteorologists were in disagreement over the forecast.
On June 3, 1944, Maureen Flavin Sweeney was working at a post office at Blacksod Point in County Mayo, Ireland. She and her husband Ted were tasked with making weather observations every hour, 24 hours a day, to relay their findings to the British Meteorological Office. During the early morning hours of June 3, also her birthday, the 21-year-old weather observer noted a drop in atmospheric pressure. Blacksod Point was a crucial observing point for meteorologists, thanks to its location in extreme northwest Ireland. The first signs of any storm approaching storm systems would be felt here— and that's exactly what Maureen's observations showed.
When meteorologists received her report via secret telegraph, they immediately phoned Maureen to confirm her report. She was asked to carefully check the observations, which she confirmed were correct. The findings led the Allies’ chief meteorologist James Martin Stagg to conclude June 5 was unfavorable for the operation. General Dwight D. Eisenhower delayed D-Day to June 6.
The forecast ultimately verified strong winds and overcast skies along the coast of Normandy. On June 4, Maureen's 1 p.m. observation noted increasing pressure, a sign that the weather was improving. Once again, Stagg was able to relay a favorable forecast to Ally commanders.
In the 1940s, meteorologists did not have satellite imagery, Doppler radar, computer models, or other modern technology we use to forecast the weather today. Weather observations and hand-drawn maps were the predominant tools weather forecasters used to determine the future conditions. A major turning point in World War II hinged on the weather observations of a 21-year-old woman.
Maureen Flavin Sweeney wouldn't know the role her reports played in D-Day until a decade later. According to The Associated Press, it wasn't until 1956, when she received a copy of the data from Ireland’s meteorological service that informed the D-Day weather forecasts. In 2022, she was honored with a medal from the House of Representatives, showcasing her work's importance.
Maureen Flavin Sweeney died on December 17, 2023 at the age of 100.
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