The only thing the AIP has to say about it is in AIP ENR 1.1 para 8.8.5.2-

[i]"When thunderstorms or there associated severe turbulence or their a probability is forecast at the destination, sufficient additional fuel must be carried to permit the aircraft to proceed to a suitable alternate or to hold for:
a. 30 minutes when the forecast is endorsed INTER; or
b. 60 minutes when the forecast is endorsed TEMPO."[/i]

There is no mention of towering cumulus so I would say that they would not impose an OPR as far as the AIP or the exam is concerned. However, of course the pilot has always got the option of carrying alternate fuel no matter what the TAF might say.

G'day
I have a question about the requirements of an enroute alternate aerodrome. For a non-EDTO flight, does it have to be within 60 minutes flight time with one engine (assuming a twin). Is there a reference for this in the CAO/CAR/CAAP?

And my second question is...
You are flying from Airport A to Airport B (non-EDTO). The flight time is 3 hours. Airport A is CAVOK and Airport B is CAVOK but all the airports in between have fog. Can you depart? References would be greatly appreciated.

Thank you for your time.