Effects of Cloud Cover
on forecasted temperatures
During the day, the earth is heated by the sun.
If skies are clear,
more heat reaches the earth's surface (as in the diagram below).
This leads to warmer temperatures.
However, if skies are cloudy, some of the sun's rays are reflected off
the cloud droplets back into space.
Therefore, less of the sun's energy is able
to reach the earth's surface, which causes the earth to heat up more slowly.
This leads to cooler temperatures.
When forecasting daytime temperatures, if cloudy skies are expected,
forecast lower temperatures than you would predict if
clear skies were expected.
At night cloud cover has the opposite effect.
If skies are clear, heat emitted from the earth's surface freely escapes
into space, resulting in colder temperatures.
However, if clouds are present, some of the heat emitted
from the earth's surface
is trapped by the clouds and reemitted back towards the earth.
As a result, temperatures decrease more slowly than if the skies were
When forecasting nighttime temperatures, if cloudy skies are expected,
forecast warmer temperatures than you would predict if clear skies