D-Day +60 Forecast

From the United States Air Force Europe Operational Weather Squadron, the weather forecast for the Normandy area for the 60th anniversary of the D-Day landings.

Update 3 Jun 2004: Are the weather guys hedging their bets?

Today's outlook calls for a spell of light rain and fog on Friday morning, a time previously expected to be just 'mostly cloudy'. Given the minimum conditions needed for parachute drops the following day, this negative trend does not bode well...

(Que foggy lens, wavering blur, harp-like tones, camera on backwards running clock; fade out then in again on black-and-white world...)

"...If you know the enemy and know yourself, your victory will not stand in doubt; if you know Heaven and know Earth, you may make your victory complete."

-- Sun Tzu, The Art of War

Fade in: 1944.

Sun Tzu's reference to Heaven is considered a nod to the whims of weather, an acknowledgement of it's impact on all man's efforts; a tribute to nature's callous disregard for those who would plan without consideration for it's vagaries.

Erik Brenstrum, of the Meteorological Service of New Zealand, writing on the 50th anniversary of the event, called the original D-Day weather forecast The Most Important Forecast in History:

RAIN FELL FROM overcast skies and gale force winds drove large waves on to the beaches of Normandy as dawn broke on Monday June 5, 1944. To the Germans watching their defences, there was nothing to show that this was the moment the Allied Armies had planned to invade Europe. In fact, the operation had been put on hold because the bad weather had been forecast 24 hours before. Had it gone ahead in these conditions, the invasion would have been a catastrophic disaster.

Nevertheless, the invasion had to occur on either the 5th, 6th or 7th of June to take advantage of the right conditions of moon and tide. Darkness was needed when the airborne troops went in, but moonlight once they were on the ground. Spring low tide was necessary to ensure extreme low sea level so that the landing craft could spot and avoid the thousands of mined obstacles that had been deployed on the beaches. If this narrow time slot was missed, the invasion would have to be delayed for two weeks.

The decision to postpone the invasion for 24 hours had been taken by Eisenhower and the Supreme Command at 0430 on Sunday June 4. It was not taken lightly, because so many ships were already converging on Normandy that the risk of detection was grave.

Nor had the forecast which prompted the postponement been easily arrived at. Eisenhower's weather advice was provide by Group Captain Stagg, a forecaster seconded from the British Meteorological Office who was coordinating the advice of three forecasting teams: one from the Meteorological Office, one from the Admiralty and one from the United States Army Air Forces.

The advice of these groups was often diametrically opposed. The American team used an analog method, comparing the current map with maps from the past, and were often over-optimistic. The Meteorological Office, aided by the brilliant Norwegian theoretician Sverre Petterssen, had a more dynamic approach, using wind and temperature observations from high altitude provide by the air force, and were closer to the mark.

The decision to invade on Tuesday June 6, taken late on Sunday night and finally confirmed early Monday morning, was based on a forecast of a short period of improved weather caused by a strengthening ridge following the front that brought Monday's rain and strong winds. In the event, Monday's bad weather had already given the Allies a crucial advantage: it had put the Germans off guard.

More to come...