If you operate an aircraft on the basis that the TAF is 100 percent correct without a plan B you WILL be caught out sooner or later.
From a practical point of view, I agree 100%.
How about from the legal point of view, assuming your statement if correct? Why are operators fuel policies not required to make provision for such instances?
The next dilemma is which alternate should be used from a flight planning perspective? Should it have been YPED, YMML, YPWR or YMIA? Which one should be nominated? As we have seen, two separate airfield had unforecast deterioration below the lowest available landing minima.
The only viable solution in this case was simply to "gas it up" to MLW on the basis of CAVOK forecasts.