The 70th anniversary of D-Day, considered the greatest invasion ever, is also the 70th anniversary of the most important weather forecast ever made.
Allied forces landed on the beaches of Normandy early June 6, 1944, but it originally was planned for a day earlier. The invasion was postponed a day due to the weather report early June 4. High winds and rain across the English Channel were forecast for June 5.
The night before the invasion, “The weather was overcast, but it didn’t look difficult,” said Herb Wood, a medic with the fighter bomber unit. “I didn’t think, as I watched the gliders go by, [that] they’ll have a tough time.”
Teams of forecasters came up with a window of opportunity between June 5 and June 7 when conditions would be prime, but they didn’t have a consensus on which day would be best. That job was left to chief forecaster Capt. James Martin Stagg.
Pilots and gliders needed good visibility, paratroopers needed winds below 12 mph, ships needed low seas, soldiers needed a low tide for dismantling any obstacles on the beach and not much rain the day before for best footing and traction.
A storm would begin intensifying nearby on June 6, but Sverre Petterssen of the Norwegian Air Force forecast the storm to slow. He relied on data from a robust network of weather stations, ships and aircraft over the Atlantic Ocean. That information proved crucial in predicting a lull in storms as high pressure moved in to the area.
“When I look at the weather and now reflect back on it, everything was planned, planned so well, that there was a feeling of security we wouldn’t be going there if the weather wasn’t receptive at this point, we wouldn’t be going right now,” Wood said.
In the end, the forecast was accurate. While not ideal, the weather was good enough.
On the beaches of Normandy the morning of June 6, 1944, started with clouds, a light breeze and 54 degrees. Pilots broke formation and flew above or below the cloud deck. Ships arrived on 5-foot waves – 32 landed and 27 wrecked. And soldiers had the wind at their back.
By afternoon, the clouds cleared and the temperature rose to 60 degrees.
“The watchfulness for the periods of weather were well advised, as we learned after we got there,” Wood said.
Among the Allied nations during World War II, the very best forecasters came together.
Stateside, detailed forecasts were prohibited, so as not to provide the enemy with conditions in the U.S.