ICAO Annex 6
2.2.3.3 Flight planning
Before commencing a flight the pilot-in-command shall be familiar with all available meteorological information appropriate to the intended flight. Preparation for a flight away from the vicinity of the place of departure, and for every flight under the instrument flight rules, shall include:
a) a study of available current weather reports and forecasts; and
b) the planning of an alternative course of action to provide for the eventuality that the flight cannot be completed as planned, because of weather conditions.
Australia AIP ENR 1.10-1
Before beginning a flight, a pilot in command must study all available information appropriate to the intended operation and, in the cases of flights away from the vicinity of an aerodrome, flights over water (see ENR 1.1 Section 62.) and all IFR flights, must make a careful study of:
a. current weather reports and forecasts for the route to be flown and the aerodromes to be used;
...
The pilot must then plan the flight in relation to the information obtained.