In 1924 Stagg became an assistant in the British Meteorological Office and he was appointed superintendent of Kew Observatory in 1939. In the winter of 1932/33 he led the British Polar Expedition of Arctic Canada. Stagg was appointed the Chief Meteorological Officer, SHAEF for Operation Overlord. In 1943 he had been commissioned a Group Captain in the Royal Air Force Volunteer Reserveto lend him the necessary authority in a military milieu unused to outsiders. Stagg worked with three forecasting teams from the Royal Navy, Met Office and the USAAF. The detail of the D-Day forecasts is in the accounts published by participants, including Stagg himself.
D-Day weather
Planners of the Normandy landings in June 1944 allowed for the tides, the time of day, and the phase of the moon – these conditions would be satisfactory on only a few days in each month. A full moon was desirable, as it would provide illumination for aircraft pilots and have the. The landings would be shortly before dawn, mid-way between low and high tide, with the tide coming in. This would improve the visibility of obstacles on the beach, while minimising the amount of time the men would be exposed in the open. Eisenhower had tentatively selected 5 June as the date for the assault. However, on 4 June, conditions were unsuitable for a landing: high winds and heavy seas made it impossible to launch landing craft, and low clouds would prevent aircraft from finding their targets. Stagg met Eisenhower on the evening of 4 June. He and his meteorological team predicted that the weather would improve enough for the invasion to proceed on 6 June. The next available dates with the required tidal conditions would be two weeks later, from 18 to 20 June. Postponement of the invasion would have required recalling men and ships already in position to cross the Channel, and would have increased the chance that the invasion plans would be detected. After much discussion with the other senior commanders, Eisenhower decided that the invasion should go ahead on the 6th. A major storm battered the Normandy coast from 19 to 22 June, which would have made the beach landings impossible. Allied control of the Atlantic gave Allied meteorologists an advantage in the North Atlantic weather war for storm prediction. As the Luftwaffe meteorological centre in Paris was predicting two weeks of stormy weather, many Wehrmacht commanders left their posts to attend war games in Rennes, and men in many units were given leave. German Commander Field Marshal Erwin Rommel returned to Germany for his wife's birthday and to meet with Hitler to try to obtain more Panzers. For his invaluable services over the D-Day period, Stagg was appointed an Officer of the US Legion of Merit in 1945 and was also appointed Officer of the Order of the British Empire at the same time.
