Weather minima for alternate airport
 

Once you airborne and arrive to destination your dest is closed.
What is your planing consideration for alternate.
For example if yor altn is cat 3 and weather is just above minima, could you take ti as alternate, or you should find another one.
But by euops.

Alternate minimums are for planning purposes only. Do whatever is appropriate for that situation.

Once you are "in flight", planning minima will not be used anymore and you must evaluate the actual situation (weather, fuel, Maintenance assistance, Airport facilities etc.).
In the aforementioned situation, I would look for another alternate :}

In my part of the world any time your destination is below alternate criteria you require an alternate. End of story.

Even though you will get in using cat 3 autoland, you must hold a viable alternate to attempt the approach. These are the rules in Oz.