D-Day was the name given to the June 6, 1944, invasion of the beaches at Normandy in northern France by troops of the Allied Forces during World War II. The goal was to cross the narrow, often stormy, English Channel into Nazi-occupied France.
The successful D-Day invasion required a combination of environmental factors: initial invasion around sunrise and at at low tide; nearly clear skies; at least 3 miles of visibility; close to a full moon; relatively light winds; non-stormy seas; and good conditions persisting for at least 36 hours and preferably for four days. To make the task of forecasting even more difficult, the Allies needed at least two days advance notice of these conditions —and because the science of meteorology was only just beginning to modernize, at the time this was a nearly hopeless task.
Krick strongly advocated for analog forecasting. The British Royal Air Force team was led by Sverre Petterssen, who was an expert in the science of air masses, cyclones and upper air patterns. His co-leader was C.K.M. Douglas, who made forecasts by interpreting weather maps and pattern recognition. Reginald Sutcliffe, the British scientist who laid the groundwork of modern weather forecasting, also worked on the D-Day forecast.
While the weather forecasters initially suggested June 5, they realized that a one-day postponement would offer better conditions. This prompted Eisenhower to invade on Tuesday, June 6. German meteorologists did not predict the clearing on the morning of the invasion, adding to the Allies’ advantage.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on Wisconsin Public radio at noon the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.
