I seem to remember reading at the time of the Wiggins hour record that the distance is heavily influenced by atmospheric pressure. Makes sense, that's why you might consider trying at altitude. But even at sea level, success or failure could be decided by whatever pressure there happens to be on that day.
Here we are from cyclingnews
"A lot of the hour record is dictated by temperature and air pressure. Air pressure is everything," he recently told Sky Sports. "I'm not a weather man, but if you have really low pressure, under 1,000 [grams per cubic metre], you will travel a lot further on the day – anything up to one kilometre for the same power. The weather forecast for the first week in June is abnormally low pressure for London for that time of year, which is fantastic."
With the athlete responsible for over 90% of the drag as they punch a hole into the air at over 50km/h, air pressure can significantly affect the power output during an Hour Record attempt and so affect the final distance a rider is able to cover.
"As the speed increases, the air resistance and drag becomes fundamental because it grows quadratically from the speed. That's why even tiny variations of the air pressure can have a huge importance," Giovanni Tredici, the Giro d'Italia race doctor and a member of Francesco Moser's 1984 Hour Record attempt staff told Gazzetta dello Sport.
An area of low pressure (1015mb) is forecast to pass over Britain on Friday but high pressure (1034mb) is forecast for Sunday when Wiggins makes his Hour Record attempt, perhaps reducing his chances of beating Boardman's record.
I read elsewhere that it was actually 1036 mBar (compared to Dowsett's 1007 mBar.
I don't know what the atmospheric pressure was in Berlin last week*, According to
https://www.timeanddate.com/weather/germany/berlin/historic pressure was hovering about 1000 mBar on 27th Feb when Ganna rode just under 4:02. Could it be that improved aerodynamics etc
and low air pressure created the perfect storm for fast times at the WC?