You would have to be out of your mind to takeoff with a forecast increasing headwind..........
Agreed, but I did say .......
......unforecast increasing headwind.
and what about the " bit for Mum " do you keep it to the end, or use it enroute ?
One of our guys was approaching New York and was advised of a 45 minute hold, and experience was that such delays usually lengthen, so had he continued he would, eventually, have still been airborne in the hold below the minimum reserve fuel required, so diverted to Boston, where the weather was worse, but manageable. Arriving Boston the weather had deteriorated below limits. Had he continued to New York he would, most likely, have by then landed without trouble - but been "illegal"; he has now no alternate fuel left, having used it diverting, and almost used his 'bit for Mum' and has nowhere to go - but he had done everything 'by the book' and was 'legal'. - but nearly dead. Eventually ATC managed to get him into a Military airfield nearby.
Don't pick me up on detail, many moons ago, can't remember all the figures, but the point is that despite ones' best efforts Murphy is always with us.