A Lesson in Radiational Cooling

Well of course these nights are cold! Why are we experiencing these cold temperatures?

The weather scene is perfect for what we call radiational cooling, but let me first explain what hinders radiational cooling. During the day the ground heats up from absorbing the shortwave radiation from the sun, but the ground doesn't gain any energy once the sun sets. At night the ground emits longwave radiation (energy), but clouds aid in keeping the heat (energy) in the lower levels of the atmosphere. This event will allow the night-time temperature to level-off as oppossed to decreasing dramatically. Now our forecast tonight doesn't involve clouds so nothing will hold back the energy removed from the ground. The clear skies will allow the energy to lost from the low levels of the atmosphere.

Also, high winds will cause the lower level temperature to remain in the lower level. Think of this as a big mixing bowl. The ground's temperature won't be able to leave the lower levels as effieciently as calm winds. Calm winds act as a quick escape for the ground's energy. Our forecast tonight include calm winds.

So tonight will be cold. Break out the winter quilts and turn on the heater because tonight we will experience textbook longwave radiational cooling.

****Also, tomorrow premiers the 1st episode of "The Tanner Cade Hour minus 55 minutes or so" on www.wdam.com. This is my show for a once-a-week episodes (web only).

tcade@wdam.com