Dragun,
There are rare occasions where we are left in no mans land. Example: short sector, on descent, ATIS suddenly indicates unforecast FOG - no fuel to go any where, TTF SPECI not yet issued. This is the occasion where we are paid to make a sensible decision, which WILL mean a PAN call and MAY mean an autoland.
In 35 years domestic flying in OZ, there has only been 1 occasion where I have made a PAN call on the basis of totally unforecast weather (FOG) and no fuel to go anywhere. There was absolutely no issue with CASA (because the forecasting system failed abysmally) or the company (because the dispatch system relied on the same data).
Sometimes you have to bite the bullet and just do it. That's the system.
The weather (INTER/TEMPO/ALTERNATE) requirements are fixed and do apply at any time. For the most part, you get a feel for weather situations and obtain TTF's frequently if it warrants.