[--MAIN HOME--] [--ALL HABYHINTS--] [--FACEBOOK PAGE--] RADIATIONAL COOLING AND OVERNIGHT LOW TEMPERATURE METEOROLOGIST JEFF HABY Temperatures tend to be the warmest during the day and the coldest at night. The radiation budget is the key reason this occurs. During the day, solar radiation is absorbed by the ground surface and this causes an increase in temperature. Once the sun goes down, this accumulative warming from solar radiation ends and the temperature starts to cool. The temperature at night not only cools because of the loss of solar radiation but also because the ground surface emits longwave radiation. The emitting of this radiation causes a slow cooling of the ground surface that is cumulative overnight. Thus, the coldest temperatures typically occur close to sunrise. Weather and surface conditions can help maximize radiation loss and/or surface cooling. These include clear skies, long nights, light wind, dry air, ground surface cover type (snow, less vegetation), and being in a valley. The next Haby Hint will examine how each of these factors contributes to the cooling.