Looks Like Rain

How weather forecasting got good.

- Hannah Fry

At four-fifteen on the morning of June 4, 1944, Group Captain James Martin Stagg, a meteorologist for the British military, arrived at the library of a grand manor house on the southern coast of England. On the other side of the room was General Dwight D. Eisenhower, the supreme commander of the Allied Forces—the man Stagg needed to convince that D Day should be postponed.

The conditions for the launch had to be just so: a full moon for visibility, low tides to expose the underwater German defenses. That left a narrow window of just three days in June, and June 5th was the date the generals had settled on. But the Allies’ warships and aircraftwould also need calm seas and clear skies, and here Stagg and his team had foreseen a problem.

Even though the skies outside promised a bright morning, the meteorologists calculated that a parade of storms was poised to barrel across the Atlantic, hampering the prospects of success. The generals were wary of any Meteorology is so ubiquitous that it is easy to overlook its monumental achievement: the power to predict the future. delay, but Eisenhower reluctantly agreed to hold off.

A few hours later, Stagg had better news. Allied weather stations were reporting a ridge of high pressure that would reach the beaches of Normandy on June 6th. The weather wouldn’t be ideal, but it would be good enough to proceed. Eisenhower gave the order to reschedule the invasion.