Your estimation of cloud cover is subjective, but scientifically important. Meteorologists and climate scientists must have accurate cloud cover observations to correctly account for the amount of solar radiation which is reflected or absorbed before sunlight reaches Earth’s surface, and the amount of radiation coming from Earth’s surface and lower atmosphere which is reflected or absorbed before it can escape to space.
When observing cloud cover, including contrails, estimate the total cover of the whole sky and at each level (low, mid, and high levels). It may be helpful to divide the sky in 4 quadrants (North, South, East, and West) and estimate cloud cover in each, then take the average to get the whole sky value.
Observer the sky overhead, excluding the horizon. This can be done by:
- Observing above 14 degrees
- Or holding your arms out in a "V," hands even with the height of the top of your head, and observing between your hands
- Or hold you fist out at arm's length, bottom even with the horizon; put your second fist on top of the other, observe the sky from above the top of your second fist.