WEATHER REPORTS KEEP D-DAY PLANNERS ON PINS AND NEEDLES

Southwick House near Portsmouth, England • June 5, 1944

Weather conditions over France’s Normandy beaches on inva­sion day, D-Day, ten­ta­tively set for this date, June 5, 1944, had to be as ideal as pos­si­ble before Supreme Allied Com­mander Gen. Dwight D. Eisenhower would issue the “go” signal for the largest sea, air, and land inva­sion ever executed. Oper­a­tion Over­lord could be likened to a huge enter­prise rotating around its D‑Day axis. It was so mam­moth that many of the most time-criti­cal parts had to begin 3 days before D‑Day and last through D‑Day+2. All across the United King­dom stock­piled mili­tary mate­riel (artil­lery, ammu­ni­tion, vehi­cles of every type) and tens of thou­sands of fighting men—Amer­i­can, Cana­dian, and British sol­diers, sail­ors, and pilots—had assembled at their embar­ka­tion points in South­ern England. More than 5,000 ships, hun­dreds of landing craft, and thou­sands of air­craft were at the ready. The fly in the oint­ment was June’s weath­er fore­cast. It unset­tled Allied inva­sion plan­ners as May’s had not. Back then a world­wide short­age of landing craft had stalled a D‑Day launch penciled in for May.

The first 7 days of June 1944 began to look iffy due to pre­dicted bad weath­er moving east over the Atlan­tic Ocean toward the British Isles and Europe. If early June’s launch was scrubbed, the launch would be pushed out to mid-June. Suit­able con­di­tions for mounting an inva­sion in­cluded a late-rising full moon, calm seas for landing craft to cross the English Chan­nel, low tide so demo­li­tion crews and frog­men could dis­able half-hidden beach obsta­cles and mines, gentle breezes for the beach assault, and skies tol­er­a­bly clear of low cloud cover for bomber crews to bomb Nor­mandy’s beaches and gun case­ments as well as for troop carrier pilots to identify their drop or landing zones. Also, the mid­night sky had to be dark enough to safely drop thou­sands of para­troopers behind the invas­ion beaches. Yes, Eisen­hower needed as many of these con­di­tions (and more) in his D‑Day quiver to ensure a successful outcome.

The invasion planners turned to British mete­o­rol­ogist RAF Group Captain James M. Stagg, a Scots­man who was Eisen­hower’s chief mete­o­rol­ogical offi­cer, to pre­dict June’s weather. A series of oral weath­er reports, 7 to be exact, were given the planners between May 29 and June 5, 1944, before Eisen­hower had suf­fi­cient con­fi­dence to begin the lib­er­a­tion of Nazi-occupied Western Europe. In his first pre­sen­ta­tion to the planning com­mit­tee and their chiefs of staff on May 29 Stagg had hedged his fore­cast bets, saying weather “dis­turbances” that were forming over the English Chan­nel might or might not have any effect on Oper­a­tion Over­lord. Four days later (June 2), in his second pre­sen­ta­tion, Stagg pre­dicted low clouds and strong winds, espe­cially toward the end of his 5‑day fore­cast; how­ever, his fore­cast was more hybrid because British and American mete­o­rol­ogists dis­agreed with one another. That evening, in his third pre­sen­ta­tion, Stagg delivered a dire fore­cast: heavy cloud cover and strong winds. The fate of June 5 as D‑Day appeared at stake.

Stagg’s June 3 pre­sen­ta­tion to the planning com­mit­tee was a downer. The previous evening’s fears about the weather were con­firmed anew by all 3 fore­casting centers. From June 4, 1 day before D‑Day’s schedu­led kick­off, strong winds blowing 13–17 miles/­21–27 km an hour up to 25–30 miles/­40–48 km an hour were fore­cast until Wed­nes­day, June 7. Low clouds down to 500 ft./­152 m would limit visi­bil­ity to 3–6 miles/­4.8–9.6 km. Eisen­hower declared a D‑Day delay.

On the evening of June 4 Eisenhower made the biggest deci­sion of his career. Stagg’s second fore­cast of the day pre­dicted improved weather lasting from the night of June 5 to the evening of June 6; a 24‑hour gap in weather fronts, take it or leave it. Eisen­hower polled the room. Mont­gom­ery, chief planner of the D‑Day inva­sion, said: “I would say go.” Walter Smith, Eisen­hower’s chief of staff, told his boss: “It’s a helluva gamble but it’s the best possible gamble.” The rest of the assembled men fell in line. June 6 became D‑Day.

Disturbing Weather Reports Play Havoc with D‑Day Launch

Above: Supreme Allied Commander Dwight D. Eisenhower and his air, land, and sea com­manders—as well as their chiefs of staff—wrestled with the Normandy inva­sion date. From left to right are U.S. Lt. Gen Omar Brad­ley, British Adm. Ber­tram Ram­sey, British Air Chief Marshal Arthur Tedder, Eisen­hower, British Gen. Bernard Law Mont­gomery, British Air Chief Marshall Traf­ford Leigh-Mallory, and U.S. Lt. Gen. Walter Bedell “Beetle” Smith. Tedder was deputy com­mander of the Allied Expe­di­tionary Force under Eisen­hower. Smith served as Eisen­hower’s chief of staff at Supreme Head­quarters Allied Expe­di­tionary Force (SHAEF). Eisen­hower chose Bradley to com­mand the U.S. 1st Army, which along­side the British 2nd Army, made up Mont­gomery’s 21st Army Group. Bradley com­manded 3 corps directed at 2 Amer­i­can inva­sion beaches, Utah and Omaha. Mont­gomery was given respon­si­bil­ity for planning the D‑Day inva­sion. He commanded all Allied ground forces (U.S., British, Cana­dian, and Free French) during Operation Overlord.

Above: Radio operators from the Women’s Auxiliary Air Force and the Royal Air Force record mete­o­rol­ogical reports sent in from air­craft and ships in the eastern Atlantic—even from a post­mistress who worked a joint post office-weather station in Western Ire­land—to the cen­tral fore­cas­ting sta­tion at Dun­stable, Bed­ford­shire, where the RAF’s weather team was stationed. The U.S. Army Air Forces mete­o­ro­logist group worked at London’s Bushey Park and the Royal Navy’s team worked down the road from South­wick House, Eisen­hower’s advance com­mand post near Ports­mouth, where his planning group met in a large mess room with comfy sofa and chairs. All 3 mete­o­rol­ogist teams pro­vided Stagg with con­stant weather up­dates, which he ana­lyzed, recon­ciled as needed, and delivered in a con­sen­sus report to Eisen­hower between May 29 and June 5, 1944. Inter­estingly, the British public never knew what the weather would be like any­where, any­time. News­papers and radio stat­ions were pro­hibited from dis­cus­sing weather news lest the enemy find something useful in it.

Left: Stagg’s weather chart for 1 p.m. GMT on June 6, 1944, shows a break in the storms raging over the English Chan­nel. The United King­dom and the Euro­pean con­ti­nent from Scan­di­na­via to Spain and a por­tion of North­west Africa appear close to the right border in Stagg’s weather chart.

Right: Eisenhower speaks to paratroopers of the 101st Air­borne Divi­sion before their jump into Normandy. Eisen­hower delayed the long-awaited inva­sion of North­western France for 1 day to pro­vide better weather conditions for the airborne drop.

Contemporary Colorized Footage of D-Day, June 6, 1944 (You may want to mute the music)