The data was gathered considering the “feeling” of weather. Only daytime values are included in the graph, as the nights are usually spent inside anyway.
The sunlight and rain are measured in hours considering times from 7am to 9pm (14 hours). Since it doesn’t matter how much rain comes down, the amount of downfall is discarded. There is no time-restriction for sunlight, since there is less sunlight in winter and more in summer.
The windspeed for stormy and calm days are based on the Beaufort wind force scale. The weather is considered calm with windpeeds up to 19 km/h (3 Bft) and stormy days start from 75km/h (Bft 9).
The data for wind and sunlight was gathered here and data for hours of rainfall here.