BKN or OVC cloud at 1000AGL or less,
Severe Turbulance,
Visibility less than 5000m,
Any mention of Mountain Waves or
Any mention of SIGMET's in the area.
Hey Richard, don't be afraid cancel and to pick another day to fly if these conditions feature in your area.... I'd even hum and ha about taking off in MOD Turbulence. Remember, we are recreational pilots who for it for the fun of it. It's no fun in those conditions. Learn about the minimums required for VFR flight, stay in VMC. Learn to read the aviation forecasts, ARFOR's and TAF's, they are your friends. Better to find out from the forecast than after you get into the air. It is good airmanship to fly another day if the conditions are no good or marginal. Besides, it is mandatory to obtain a aviation forecast when leaving the vicinity of the aerodrome...... I get one before I do any flying.
Tony