Cloud cover has a significant effect on the temperature forecast. The quantity of solar energy reaching the surface is a strong determinant of surface temperature.
The troposphere is heated through solar radiation that reaches the earth's surface. Fluctuations in this solar energy change the surface temperature, where most temperature measurements are made. Clouds act as a regulator to the amount of solar radiation that reaches the surface.
During daytime, clouds reduce the temperature, depending on the cloud thickness, the cloud density and time of permanence. If more cloud cover occurs than is expected during the daytime, the surface temperature will generally be cooler than expected. If cloud cover is less than expected, the surface temperature will generally be warmer than expected. One example of this situation occurs when fog or a low stratus cloud cover is present, especially during cooler season.  A fog or low cloud deck is difficult to forecast, because it ofter forms only locally. If the fog does not dissipate when expected, the surface temperature forecast will deviate significantly.

At night, clouds have the opposite effect on temperature. More cloud cover than expected at night usually result in warmer temperatures than expected. Less cloud cover results in cooler temperatures than expected. The reason is that at night, the earth's surface irradiates energy in the form of long-wave radiation and does not receive any short-wave radiation from the sun to warm the surface. Water vapor intercepts long-wave radiation and prevents it from escaping into space. The result is warmer temperatures. During a clear night, a maximum amount of long-wave radiation will escape into space and thus surface temperatures will cool at the maximum rate for the given weather conditions.

Clouds are also carriers of precipitation. By influencing temperature, clouds have a complex effect on the condensation point. Generally, lower cloud temperatures will increase precipitation under equal circumstances. However, thunderstorms will only form if higher temperature air rises quickly  into the boundary layer (where condensation occurs). If cloud cover causes the boundary layer to be cooler than expected, this could prevent the capping inversion from being broken in a thunderstorm situation. If the cap is not broken then no thunderstorm precipitation will occur in many cases. In the opposite case, a reduction of cloud cover can enhance instability during the day and increase the thunderstorm threat.

In summary, the ability to predict cloud development and movement is fundamental to the calculation of a reliable weather forecast.