The weather on D-Day, June 6, 1944, was rough but manageable, with overcast skies, winds shifting from along the coast to slightly onshore, choppy seas, and temperatures around 14°C (57°F) along the Normandy coast. It was far from ideal for an amphibious invasion, but it represented a narrow window of slightly improved conditions between two storms, and Allied meteorologists correctly identified that window when their German counterparts did not.
The Storm That Almost Stopped the Invasion
The original invasion date was June 5, 1944. Weather observations taken in western Ireland on June 3 revealed an approaching storm moving east across the Atlantic, and General Eisenhower made the decision to delay by 24 hours. That call proved correct. On June 5, winds in the English Channel reached force 5 on the Beaufort scale, meaning sustained speeds of 19 to 24 miles per hour with waves around six feet high. Landing craft would have struggled to stay on course, troops would have arrived on the beaches soaked and exhausted, and naval gunfire support would have been wildly inaccurate.
The stakes of postponement were enormous. More than 150,000 troops were already loaded onto ships, and tidal conditions (a low tide at dawn, needed to expose German beach obstacles) only aligned on a handful of dates each month. If June 6 didn’t work, the next possible window was nearly two weeks away, raising the risk that the Germans would discover the invasion plans.
How Forecasters Found the Window
The Allied forecast team was led by Group Captain James Stagg of the Royal Air Force, who coordinated between British and American meteorologists. What gave the Allies their critical advantage was access to weather stations across the North Atlantic, including ships and outposts in Iceland, Greenland, and the open ocean. These stations allowed forecasters to track the movement of the low-pressure system that caused the June 5 storm and, more importantly, to spot a ridge of high pressure following closely behind it.
That ridge would bring a brief improvement: lower winds, reduced cloud cover, and calmer seas lasting roughly 36 hours before the next weather system arrived. Stagg presented this forecast to Eisenhower on the evening of June 4, and Eisenhower gave the order to go. The German meteorological service, which had lost access to Atlantic weather stations and relied on a less complete picture, saw only the ongoing bad weather and concluded no invasion was possible. Several German commanders actually left their posts, believing the storm made an Allied crossing unthinkable.
Conditions on the Morning of June 6
The weather that greeted Allied forces on the morning of June 6 was improved compared to the day before, but still far from calm. Winds over the Channel shifted from running along the coastline to blowing slightly onshore from the northwest, which pushed waves toward the beaches. Seas remained choppy enough to cause widespread seasickness among troops in the flat-bottomed landing craft, many of whom had been aboard ships for over 24 hours by the time they hit the beaches.
Cloud cover was heavy, with a thick overcast ceiling that caused problems for both bombers and paratroopers. The airborne divisions that dropped behind the beaches in the early morning hours were scattered far from their intended landing zones, partly because pilots had to fly above or through cloud layers that obscured the ground. Many paratroopers landed miles from their objectives.
For the bomber crews tasked with softening up the beach defenses before the landings, the cloud cover forced last-second decisions. At Omaha Beach, heavy bombers delayed releasing their payloads by seconds to avoid hitting their own troops, which meant most bombs fell harmlessly inland. The German defenses at Omaha remained largely intact, contributing to the devastating casualties there.
How Weather Shaped the Battle
The convoys that carried the invasion force set out on the evening of June 5 into force 5 winds, enduring a seventeen-hour crossing of the Channel. By the time the first waves hit the beaches at 6:30 a.m., conditions had eased somewhat, but the sea state still caused serious problems. Many of the amphibious tanks launched offshore, designed to float using inflatable canvas screens, sank in the rough water. At Omaha Beach, 27 of 29 amphibious tanks went down, leaving infantry without the armored support they were counting on.
The choppy seas also pushed landing craft off course. Units that had rehearsed specific beach approaches for months found themselves deposited hundreds of yards from their assigned sectors, mixing up carefully planned assault teams. Strong lateral currents along the beaches compounded the problem. At Utah Beach, the entire first wave landed about a mile south of its target, which turned out to be fortunate since the defenses there were lighter.
Despite all of this, Stagg’s forecast proved accurate. The weather held long enough for the Allies to establish a foothold on all five beaches by nightfall. Had Eisenhower waited for the next tidal window around June 19, the invasion would have coincided with one of the worst Channel storms in decades, a gale so severe it later destroyed the artificial harbors the Allies had built on the Normandy coast. The decision to go on June 6, based on a narrow and uncertain weather forecast, was one of the most consequential gambles of the war.
What the Germans Expected
The weather played directly into the Allied deception. German meteorologists, working with incomplete Atlantic data, forecast continued stormy conditions through early June and saw no viable invasion window. Field Marshal Erwin Rommel, who commanded the coastal defenses, left Normandy on June 5 to visit his wife in Germany for her birthday, confident that the weather made an attack impossible. Several other senior German officers were away at a war game exercise in Rennes.
When reports of Allied paratroopers began arriving in the early hours of June 6, German command was slow to respond, partly because they still believed the weather was too poor for a full-scale crossing. By the time the scope of the invasion became clear, hours of precious response time had been lost. The same rough, overcast weather that made the landings so grueling for Allied troops also provided a kind of strategic camouflage, arriving on a day the enemy had written off as impossible.