Saturday 3rd June 1944 was what one might describe as a 'typically mixed' June day across the UK and Ireland. Decent spells of sunshine affected SE England where temperatures reached 71F.
A ridge of high pressure extended from the Azores high whilst fronts traversed the UK and Ireland. A broad warm sector (the area between and warm and cold front) appears to affect most of England, Wales and Ireland. The original working chart from 7am (the green coloured land) clearly shows the forecasters attempt to analyse conditions, and how fronts are sketched, then made permanent with chinagraph pencils.
The complex low in the Atlantic south of Greenland draws attention, as does how close together and straight the isobars are west of Ireland, these foretelling of a large sea swell affecting Ireland and the English Channel.
The first entry in Chief Meteorologist Stagg's diary on this date is, "a day of extreme strain". This highlights how difficult Stagg was finding trying to reconcile differences in predictions from Widewing (the American forecasters), Dunstable and the Admiralty.
No doubt ringing in his ears were the words spoken the day before by General Frederick Morgan, Chief of Staff Supreme Allied Commander (COSSAC). On leaving the evening conference Morgan had said, "Good luck, Stagg; may all your depressions be nice little ones: but remember, we'll string you up from the nearest lamp-post if you don't read the omens right."
No pressure there then!!!!
There was some good news for Stagg though. By 5pm the Admiralty had amended their forecast to fall more in-line with the more pessimistic forecasts produced by Dunstable. They were now more certain that the ridge extending from the Azores high would collapse to the south and be less of a factor. Widewing (the American forecasters) did not agree.
There is much to tell of what transpired by the 9.30pm Supreme Commanders Meeting at Southwick House, but suffice to say here that by now the American forecasters had alerted deputy chief of staff for air, Vice Air-Marshal Robb to the fact they were more hopeful of the forecast than the British.
But in the meeting Stagg had to make the call and deliver the forecast. He said that during 4th and 5th June depressions would cause "disturbed conditions in the Channel and assault area". He forecast cloud would be low with limited visibility. Stratus cloud with a base of 500 to 1000ft and ops of 2500 to 3000ft would obscure the ground. Winds were also forecast to be gusty, hampering Navy operations.
After several more questions Stagg went outside to await the verdict. He was then told that on the basis of the weather forecast he had just deliver, D-Day would be held off for one day until 6th June 1944.
By the time Stagg went to bed in the early hours of 4th June, dawn was already beginning to glow. When he awoke and went outside in order to brief himself before the next conference at 4.45am he was concerned to find, "...a still almost cloudless sky and only a slight breeze....by our forecast it should already be overcast with a force 4 wind.
What had gone awry?"
Poor Stagg, he was experiencing every weather-mans foe...Mother Nature!
(Original Charts (c) Crown Copyright 1944 National Meteorological Library & Archive)