Most forecasts (including the BOM) have three issues you should remember:
a) "fine" only means "not raining". It doesn't mean clear sky.
b) The forecasts are generally for daytime weather conditions, not night-time; and hence forecasts are often quite wrong at night. So you shuld learn to read the synoptic map, and the satellite cloud image to predict for yourself how it will change in the next day or two (it isn't hard). AFAIK there is only 1 site that gives reasonable forecasts for night-time.
http://m.yr.no/place/Australia/New_S...ales/Katoomba/
c) there is a moderate correlation between the phase of the moon vs the presence (or lack) of cloud in the evening: the likelihood of evening cloud between third quarter and first quarter (when we observe) is higher than the likelihood between first to third quarter.