The D-Day Weather Forecast

Assault troops approach Omaha Beach, D-Day, June 6, 1944.
Source: National Archives and Records Administration.

Know the enemy, know yourself; your victory will never be endangered. Know the ground, know the weather; your victory will then be total. - Sun Tzu, The Art of War, c.400-320 b.c.

Today marks the 70th Anniversary of D-Day.  Perhaps the most important weather forecasts ever issued were for the invasion, which required a full moon, clear skies, light winds, and low tides.  The window of opportunity was small and there were no second chances.  Think about the technology at the time.  Numerical weather prediction wasn't yet invented.  There was no Internet (gasp!).  No satellite imagery.  No weather radar.  Few upper-air observations.  No computers to plot data.  Three groups on the Allied side provided forecasts, with Norwegian Sverre Petterssen playing a vital role in the successful forecast.  Nevertheless, as is often the case with history, there is disagreement amongst the participants concerning the actual events and contributions.

James Flemming, a professor of science, technology, and society at Colby College provides a brief summary in his paper, Sverre Petterssen, the Bergen School, and the Forecasts for D-Day.  It's a quick read for history and weather buffs.

Another option is Sverre Petterssen's book, Weathering the Storm: Sverre Petterssen, the D-Day Forecast, and the Rise of Modern Meteorology.

Finally, thanks to a post at the Capital Weather Gang, I just learned about another perspective from John Ross, The Forecast for D-day: And the Weatherman behind Ike's Greatest Gamble.

Personally, I'm partial to Petterssen's account, but only because he was a skier :-).