By 1944, meteorologists had learned quite a bit about the atmosphere. The advances made in forecasting were put to the test during World War II. Without the aid of satellite pictures, radar, or forecasts generated by computer, forecasters played an integral role in D-Day, the Invasion of Normandy.
Allied leaders met in Tehran, on November 28, 1943. At this historic meeting, President Roosevelt, Soviet Leader Stalin, and British Prime Minister Churchill agreed to forge ahead with plans for an Allied invasion of Europe. The British and Americans would attack German forces in northern France, while Soviet troops would launch an assault on the eastern front. The invasion, code-named Operation Overlord, would contain over three thousand assault craft, 300 warships and nearly 200,000 men. The target: a 50-mile stretch of beach along the Normandy coastline.
The date for the invasion had to take astronomical and weather factors into account. The Allies required a combination of low tides, pre-dawn twilight, and favorable moonlight. Supreme Allied Commander General Eisenhower realized that Overlord had a very small window of opportunity. Many pieces had to fall into place, and one of them, meteorology, was about to play an important part, a very important part in the world's future.
Weather balloons collected data on wind speed and direction. Developed in the late thirties, the radiosonde helped forecasters measure upper air patterns. The biggest problem was limited observations.
Eisenhower declared, "The selection of the actual day would depend on weather forecasts." The best tide and moon data gave the military three options for the invasion: late May, June 5 or 6, or June 17 and 18. Given those dates, the forecasters had to predict the best conditions for the invasion.
By April 1944, preparations for the invasion were well underway. Allied commanders were briefed daily about D-Day weather conditions. Eisenhower selected Dr. Stagg, a British civilian, and an American military man, Colonel Yates, to head a team of meteorologists who would work exclusively on the D-Day forecast. Three individual teams were formed, and they gave input to Stagg and Yates during telephoned briefings.
The US meteorologists were located in London. The British meteorological team was at Dunstable, and the British Admiralty weather forecasters were based in London. Each office would take turns in leading the briefings. By mid-May weather conferences among the three groups were held three times a day. The commanders asked the forecasters for a five-day forecast, a new discipline for many of them. They also had the added complication of having to forecast for particular days, as decided by the military.
Each military branch had different weather requirements. The Navy needed light winds, good visibility and no substantial swell in the English Channel. The Air Force required various types of cloud cover, with minimum heights for different types of aircraft. The Army needed dry ground, enough daylight, good visibility and light winds. A certain amount of cloud cover was necessary for the safe landing of paratroopers. The Army also needed low tides so the small craft and soldiers could maneuver around beach obstacles and mines.
By early May, practice drills were taking place all over the British Isles. As the troops practiced on land, the Air Force was busy flying reconnaissance missions.
This information was used by forecasters to build a picture of what the Allied forces could expect on D-Day. Eisenhower had already ruled out late May because of the lack of time to build up the vast armada. After a meeting of the Allied Commanders on May 22, the forecasters learned that the date had been set: June 5.
In his memoir, "Crusade in Europe," Eisenhower writes that the consequences of delaying the invasion beyond the June 5 window were "almost terrifying to contemplate." Secrecy would be lost, and putting the huge invasion force on hold would be a logistical nightmare.
"The tension," he wrote, "was made even worse by the fact that the one thing that could give us a disastrous setback was entirely outside our control."
As May turned to June, it looked as though his worst fears might be realized. In early June 1944, as practice drills were increased, the spring-like weather in the English Channel started to deteriorate. The Allied Commanders and the team of forecasters were about to question the 5th as a safe day to launch the invasion.
The weather briefings to the Allied Commanders increased to two a day as the outlook for the fifth became questionable. Forecasters located a cold front. They predicted it would sweep through the English Channel causing high winds and low clouds, impossible conditions for an invasion. The three forecast centers disagreed on the timing of the front, but by early Sunday they had come to a consensus. Stagg, head of the forecast team, reported to Eisenhower that the storm would sweep through on the night of June 4 and linger on into the 5th. Eisenhower ordered a 24-hour postponement. Some of the massive force was already at sea.
As troops continued to board ships, meteorologists debated over the outlook for June 6. The front had pushed well into France, but arguments continued over how rapidly the weather would clear up. The Americans said the weather would be good enough. The British Meteorological office was more pessimistic.
The Admiralty thought it was worth a chance. After a heated discussion, Stagg and Yates went with the majority vote. At 9:30 p.m. Sunday, Eisenhower made the decision: Operation Overlord was on. Although the weather was not perfect, it was now or never. The greatest invasion in modern history now hinged in large part on the accuracy of the forecast.
The invasion was launched as dawn broke on June 6. The storm cleared. Assault beaches were cloud covered but approachable. What the Commanders did not know was that the Germans were not prepared for the invasion.
German meteorologists produced their own weather maps, which differed slightly from the Allied Forces. The Germans showed a weak disturbance moving toward France on June 6. Lt. General Habermehl, head of the German Weather Service, advised that conditions were unfavorable for an Allied invasion. Field Marshall Rommel, who was in charge of the area, felt so assured that he left to attend his wife's fiftieth birthday party in Germany.
German troops along the beaches were put on stand-down. While Rommel was away, the German meteorologists amended their forecast saying the weather would clear on the sixth, but that forecast was left on the general's desk unread. Even so, the landings were far from easy. The moderate winds caused havoc for the landing craft.
Low clouds caused problems for the gliders and paratroopers. Many were dropped miles away from the original target and were captured. The battle on the beaches was fierce. Two hundred thousand troops came ashore; some did not even reach the sand. Ten thousand men lost their lives on the Normandy beaches. But the invasion was on.
Eisenhower's decision to go was an inspired one as on the next possible date, June 18, the worst storm in sixty years swept through the English Channel. Had he waited, D-Day might have been a disaster as all three teams inaccurately forecast the storm.
For one shining moment, the world's future lay in the hands of a few skilled forecasters.
