Weather is a major environmental consideration for VFR flight. As pilots set their own personal minimums, the evaluation of following weather elements is highly recommended:
1. Ceiling and Visibility
a) what are the current ceiling and visibility and how much room do I have between the reported / forecast ceilings and the terrain along my route?
b) does this information suggest any need to change my planned altitude?
c) if I have to fly lower to stay out of the clouds, will terrain be a factor?
d) where are the cloud base and cloud top?
e) are the reported and forecast ceilings above my personal minima? (Note: personal minima for a typical 50-100 hour/year private pilot should be at least basic 3000 feet for daytime flight, raised to 4000 feet for night flight in non-mountainous terrain and at least 5000 feet for Visual Flight Rules (VFR) night flight in mountainous terrain).
f) what visibility can I expect for each phase of flight (departure, enroute, destination)?
g) are there conditions that could reduce visibility during the planned flight? (Hint: look for indications such as a small and/or decreasing temperature/dew point spread).
a) consider winds at the airports being used and the strength of the crosswind component (Note: for most GA pilots, personal minima in this category might be for a maximum gust of 5 knots and maximum crosswind component 5 knots below the maximum demonstrated crosswind component) .
b) if flying in mountainous terrain, consider whether there are strong winds aloft. Strong winds in mountainous terrain can cause severe turbulence and downdrafts and be very hazardous for aircraft even when there is no other significant weather.
3. Other Phenomena
a) are there any thunderstorms present or forecast?
b) what is the forecast freezing level for this flight?
c) are there any indications for wind shear or convective activity (thunderstorms) which, apart from the possible impact on departure / approach, may indicate the possibility for turbulence to occur.
4. Aircraft performance
a) given temperature, altitude, density altitude, and aircraft loading, what is the expected aircraft performance on:
- takeoff distance,
- time & distance to climb,
- cruise performance,
- landing distance?
b) Are these performance values sufficient for the runways to be used and the terrain to be crossed on this flight? (Note: remember that it is always good practice to add a 50% to 100% safety margin to the “book numbers” you derive from the charts in the aircraft’s flight manual).
c) If icing conditions are encountered, is the pilot experienced at operating the aircraft’s deicing or anti-icing equipment? Is this equipment provided and if yes, is it in good condition and functional? For what icing conditions is the aircraft rated, if any?
After all this consider the possibility that the weather may be different from forecast. Have alternative plans and be ready and willing to divert should an unexpected change occur.