|CLOUDS ACT LIKE A BLANKET?
METEOROLOGIST JEFF HABY
The phrase "clouds act like a blanket" is used to describe warmer temperatures at night when
clouds are present
as opposed to cooler temperatures on a clear night. Clouds absorb longwave radiation
while also radiating longwave radiation to
the surface. Thus, this extra longwave energy keeps cloudy nights warmer. Keep in mind this blanket trick is only
good for the night. Clouds act more like a "heat shield" during the day. Although clouds continue to trap longwave
radiation during the day, they also reflect visible and shortwave energy from the sun to space. Visible and shortwave
wavelengths have more energy than longwave radiation. Cooling due to a reduction of visible and shortwave energy at
the surface will more than outweigh the warming due to an increase of longwave energy during the day. Thus, cloudy
days tend to be cooler than clear days, all else being equal. The amount of
cloud cover will be a big influence to the forecast.