Hi Tom . It is one single season, many . so the sample size is adequate . Talking about a season the data matrix becomes bigger because the outlook is longuitidinal  and equals the number of seasons multiplied by the months or weeks . Three years denote 18 monthly data points , four years denote 24 monthly data points . I agree  however a single season isn't enough to extrapolate /make surmising . 

Best Regards

Mohamed