Having only just become aware of this website, this is a rather late reply to your question.
I was the duty Met Observer that night and can remember the crew coming in for their briefing. I knew the co-pilot, Peter Wormall, from school days. I was not privy to the forecasts or the briefing details and never saw the BOI findings or attended the enquiry. However, I can remember that visibility was misty, about 2000 to 3000m but perfectly reasonable for take-off.
Something that stuck in my mind was the unusually strong temperature inversion in the lower layers at the time of take-off. The aircraft was fully laden with fuel and instead of having extra lift from the usually denser air aloft as it ascended (temperature usually decreases with height), the warmer and less dense air it probably experienced was a distinct disadvantage. Please remember that I was not a trained forecaster and had no input into the proceedings apart from observing and plotting tephigrams and charts.
Dave Taylor