The weather limits are lower than CAVOK...
Canada's air regs, others may vary
(2) Weather Requirements
For at least one (1) hour before and until one (1) hour after the estimated time of arrival at the aerodrome of intended landing, there shall be, in respect to that aerodrome:
(a) no risk of fog or other restriction to visibility, including precipitation, forecast or reported, below 3 miles;
(b) no risk of thunderstorms isolated or otherwise forecast or reported;
(c) a forecast ceiling of at least 1,000 feet above FAF altitude and a visibility of at least 3 miles or a ceiling of at least 1,500 feet above the MDA and a visibility of at least 6 miles; and
(d) no risk of freezing rain, freezing drizzle, or sleet forecast or reported;
Other restrictions, read
721.19 No Alternate Aerodrome - IFR Flight
Google "no alternate ifr australia" the regs are probably similar