The intensity of a blue sky varies with the seasons; strongest in Spring-Summer, weakest in autumn-winter, in the southern latitudes. In equatorial regions, the light remains fairly constant and predictable, even with sporadic clouds. A meter reading will only be affected if a large number of clouds fill the sky, thus reflecting light. Where clouds cover the sun either in hazy to overcast light, the light changes from point to diffuse, and an entirely different meter reading again will be obtained. In a nutshell there should not be a change in a meter reading just because of a few clouds, but the more clouds, the more chance of light being reflected and the greater the variation in a metered reading out in the open.