D-Day: The Weather Forecast That Changed History

And Other Ways That Weather Influenced Historical Events

By Michael Steinberg, Old Farmer's Almanac Meteorologist
June 5, 2019
D-Day Weather

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From D-Day to the American Revolution, weather has played pivotal moments in world history. Discover five surprising ways that weather changed history and shaped the course of human events!

Most of us know that it was a change in the climate, caused by an extraterrestrial impact or a massive bout of volcanism, that led to the extinction of the dinosaurs, rise of the mammals, and, eventually, emergence of humans.

But, since that time, weather and climate have also played a critical role in numerous events that have dramatically changed the course of human history. Here are—in my opinion—another 5 of the top 10 (we presented the first 5 times weather changed history last month):

1. 1812: Napoleon Defeated by Russian Winter

In 1812, Napoleon assembled the largest army Europe had ever seen, with more than 600,000 men, to attack Russia and add it to his empire. His soldiers quickly captured Moscow, but as they marched away with their spoils, the severely cold Russian winter arrived, with temperatures dropping as low as 40 degrees below zero (in both Fahrenheit and Celsius—40 below zero is the temperature at which the two scales have the same reading). As many as 50,000 horses died from the cold in 1 day and only 150,000 of the soldiers made it back to France, the rest succumbing to the cold. It was the beginning of the end for Napoleon’s empire, and heralded the emergence of Russia as a power in Europe.

2. 1815: “The Year Without a Summer” Leads to Famine, Cholera, Bicycles, Mormons, and Frankenstein

Earth was experiencing the concluding decades of The Little Ice Age in a period of relatively low solar activity from 1790 to 1830 known as the Dalton Minimum. May 1816 in particular had the lowest sunspot number (0.1) to date since record-keeping on solar activity had begun. From April 5–15, 1815, (what is now) Indonesia’s Mount Tambora produced the world’s largest eruption since a.d. 180, which ejected immense amounts of volcanic ash into the upper atmosphere, where the jet stream carried it around the world. The result was a further reduction in solar irradiance that brought record cold to much of the world during the summer.

The unusual cold played havoc with agricultural production in many parts of the world, resulting in crop failures, dramatic increases in food prices, famines, cultural disruptions, and epidemics of cholera and other diseases. Rapid, dramatic temperature changes occurred frequently, as temperatures sometimes went from above-normal summer levels to near freezing within hours. U.S. grain prices at least quadrupled, and oat prices increased almost eightfold.

Elsewhere around the world, famine, riots, arson, and looting occurred in many European cities, while China suffered from massive crop failures and disastrous floods and a disruption in the Indian summer monsoon spread a cholera outbreak from a region near the River Ganges all the way to Moscow.

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Image: The dust from the 1815 eruption of Mount Tambora in the Dutch East Indies (now Indonesia) caused a worldwide lowering of temperatures during the summer of 1816, when the Almanac, legend has it, inadvertently but correctly predicted snow for July. Culver Pictures

“The Year Without a Summer” also had cultural effects:

  • The lack of oats to feed horses likely inspired German inventor Karl Drais to research new ways of horseless transportation, which led to his invention of the precursor to the bicycle.
  • Many Americans left New England for the Midwest, accelerating the westward movement of the American people. Vermont alone had as many as 15,000 people emigrate, including the family of Joseph Smith, who moved from Norwich, Vermont, to Palmyra, New York. This move may have made possible the publication of the Book of Mormon and the founding of the Church of Jesus Christ of Latter-day Saints.
  • In June 1816, Mary Shelley was forced by the weather to spend her Swiss holiday indoors with her literary companions, where to pass the time they decided to have a contest to see who could write the scariest story. The result was the novel Frankenstein; or, The Modern Prometheus.

The Old Farmer’s Almanac also might have predicted “The Year Without a Summer”! Find out about this legendary Almanac story and how “The Year Without a Summer” occurred.

3. 1588: England Propelled to World Dominance After Hurricane Destroys Spanish Armada

The defeat of the Spanish Armada in 1588 has been called one of the most decisive battles in Western civilization. In 1588, King Philip of Spain sent an armada to collect his army from the Netherlands, where they were fighting, and take them to invade England. However, the wind didn’t cooperate with his plans.

After about 2 weeks of battle, the Spanish fleet had been badly damaged and began to make a retreat. As the Armada reached the latitude of Ireland, it encountered a major hurricane. Hammered by the wind and sea, at least 24 ships were driven ashore on the Irish coast, where many of the survivors were killed by Queen Elizabeth’s troops.

The defeat of the Spanish Armada was the key event that propelled England to become the world’s dominant power for the next three centuries.

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4. 1944: D-Day is Successful Due to Better Weather Forecasts Than Germans

Perhaps the best known and most important weather-related event of World War II was Hitler’s failed Russian invasion of 1941. He waited until June 22 to start the invasion, expecting a quick victory, but when Moscow held out until winter, the severe cold defeated Hitler just as it had defeated Napoleon more than a century earlier.

But it was the success of a D-Day weather forecast (June 6, 1944) that may have played a critical role in winning the war. You might say it was the most important weather forecast in world history.

D-Day was originally set for June 5. The Allied forces’ invasion of France across the English Channel would give them the foothold needed to defeat the Germans by the following May. 

However, forecasted storms on the 5th forced allied leader Gen. Dwight Eisenhower to reconsider the timing of the invasion. Without a break in the weather, D-Day would have to be put off two weeks until tides and moon were right again. 

Critical decisions about when to send the Allied forces across the channel were based on weather forecasts compiled by Allied meteorologists, which predicted a break in the unfavorable weather on June 6. It was Eisenhower’s chief meteorologist, Group Capt. James Martin Stagg, who had advised the postponement of the the invasion of Normandy by one day over protests from his fellow meteorologists; they felt the weather would be good enough for the mission to take place. 

Eisenhower launched the invasion for June 6 with a simple: “OK, we’ll go.” The Allies made the right call. It turns out that June 5 did indeed bring high winds, heavy seas, and stormy conditions which would likely have caused the invasion to fail and set world history on a different course. And if they had waited the two weeks later (for the right tides and Moon), they would have been faced with an unforecasted heavy gale. It’s very possible that the Allies’ victory would have been delayed by a year or the Soviet Union would have taken control of the continent.

In addition, the Allies had broken Germany’s secret Enigma code, which enabled them to gather and use weather observations from German territories in making their forecasts, as well as to see that the Germans had forecast weather conditions to remain unsuitable for an Allied assault on June 6.

This gave the Allies’ meteorologists extra information to advise that conditions would be marginal but sufficient to launch the invasion. 

Years later, when President Eisenhower was asked why the Normandy invasion had been so successful, his answer was:  “Because we had better meteorologists than the Germans!”

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5. 1776: Fog Allows Washington to Avoid Defeat, Keep American Revolution Alive

The American Revolution almost ended with defeat by the British in the summer of 1776, when Gen. George Washington was leading 19,000 troops in the defense of New York City that summer after the British had increased their troops on Staten Island to 40,000.

Not sure where the British would attack, Washington left half of his forces in lower Manhattan and moved the rest to Brooklyn and Queens. On August 27, the British began an attack on Washington’s Brooklyn and Queens positions, charging the American defenders with overwhelming force.

Under the cover of darkness and with the help of some locals, the Americans managed to slip away unnoticed to Manhattan via the East River, with General Washington himself one of the last to retreat to safety. The British, stationed only a few hundred yards away, were totally unaware of the movement because of a dense fog that had formed in the early hours of the morning.

If not for that fog, Washington likely would have been captured and the American Revolution would have ended in defeat, with its leaders hanged as traitors.

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Now read about five more ways that weather changed history!

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