D-Day Was W-Day
This past weekend was the Impact A Hero weekend here in Houston (Sugar Land, actually). It’s an annual celebration honoring wounded veterans and includes a 5K run/walk/wheel, a golf tournament (happening as a type this) and a Hall of Fame Gala that happened last night. The gala was inspirational. As we in the audience listened to the stories of how these soldiers, airmen, sailors, and Marines had been terribly injured, their stories of survival and their positive vision of the future, we couldn’t help but applaud — loudly, often and standing.
It had been a long time since I’d been so immersed in a military event and with today being the 67th anniversary of when the Allied forces invaded Normandy (D-Day), still the largest amphibious invasion in the history of the world, I couldn’t help but think not only about our wounded veterans of today, but of our wounded veterans from World War II, Korea, Vietnam — all of our wars. It seems that no matter how war changes over the decades and centuries, one thing remains constant: the wounded. If you’re looking for a veterans organization to be involved with, check out Impact A Hero.
Speaking of the military… YourWeatherBlog is, of course, a weather blog so I would be remiss if I didn’t also mention perhaps the most important weather forecast in history, as it happened on this day, 67 years ago. Or rather, it happened in the days immediately prior to D-Day in support of the D-Day invasion. There have indeed been tremendously important forecasts in the decades since — and not just military forecasts. In almost any field of aviation, marine, agriculture, industry, climate and many more, critical weather forecasts happen almost daily — often with millions of dollars and many lives on the line (a single hurricane forecast for the Gulf of Mexico can result in thousands of hands being evacuated and millions of dollars in lost revenue), but it is the rare forecast that puts so much on the line as the D-Day forecast of June 6, 1944: more than 160,000 troops were to invade the coast of northwest France while facing the tremendously fortified German occupational forces who were expecting the assault.
Or were they?
If you’re a military strategist, what would be your most ideal weather for an invasion? It’s not really weather, but the cover of darkness would likely be first on your list. Cloudy skies would be a plus, wouldn’t they? A moon, especially a full one, would not be ideal because for all practical purposes, it would light up your invasion force like the sun. And what about tides? A low tide means your forces would have a longer time to be exposed to German gunfire while on the beach; high tide means a shorter beach but what about mines? And if you could pick, what type of wind would you choose? Windy conditions would make the seas choppy and wreak havoc with the airborne troops and gliders.
The Allied strategists had to consider the best weather for all the forces of the invasion, which might actually run counter to what you’d suspect to be the best forecast. First, cloudy skies were not favored because a large number of invading troops were being delivered by air — both by glider and by parachute. The best visibility was needed for both air and land operations, so a full moon with few clouds was desired. Additionally, the full moon would result in low tides at Normandy which, combined with the best nighttime visibility, would make avoiding mines and other obstacles possible.
The planners laid out the weather requirements in four scenarios, then assigned odds against occurrence to each:
(a) D-Day to be within the period of one day before to four days after new or full moon;
(b) D-Day itself to be quiet and followed by a sequence of three quiet days;
(c) Clouds to be less than 3/10 cover below 8,000 feet and visibility more than 3 statute miles, OR
(d) Cloud base generally above 3,000 feet and with morning mist or fog not excluded.
Timing, as they say, is everything. Once the needed weather criteria was determined, the Allied forecasters needed to properly time the weather patterns to be most advantageous for the invasion. As a strong Atlantic low pressure moved through the region, it was thought the invasion would need to be cancelled. Yet on the strength of a single forecast by British Royal Air Force Chief Meteorologist James Stagg, the invasion was not cancelled but delayed by one day. (Sverre Pettersen, a Norwegian meteorologist, is also attributed to the critical forecast.)
Overall, the invasion was considered a success and history considers it the turning point of World War II. Generally the forecast was considered a success as well, however cloud cover was not ideal and Allied air forces were not able to destroy many German strongholds. On the other hand, German weather forecasters did not expect a break in the poor conditions and German soldiers and officers were caught unaware as the invasion began. In fact, it’s well known that German Field Marshall Rommel had taken advantage of the poor weather to return home to celebrate his wife’s birthday.
D-Day is the term used in military planning to denote the day in which an attack or invasion is to occur. The most famous D-Day of course, is the Normandy Invasion. For those of us in the weather business, June 6, 1944 is also W-Day — Weather Day — for not only denoting a tremendous forecast, but also marking the beginning of modern day weather forecasting.
Some are weatherwise, some are otherwise. –Benjamin Franklin