Temperatures this afternoon ran 5 to 10 degrees below average, all thanks to the thick stratus clouds we saw this morning! Dry air worked across Arklahoma allowing the clouds to decrease throughout the morning and early afternoon.

Tonight we look for radiational cooling to occur. Our Wednesday morning will feel more like early October. The graphic below shows where our average overnight low should be this time of the year. Here are some things to consider when forecasting for radiational cooling.



Clear sky- When skies are clear the longwave radiation is better able to escape into space. When clouds are present the clouds will reflect and emit longwave radiation back to the surface. With clouds there is less net longwave energy escape. It is ideal to have a clear sky all night.


Dry air- Even when skies are clear, water vapor in the air will absorb and emit longwave radiation. Humid air can act like cloud cover when it comes to longwave energy trying to escape. It is ideal to have low dewpoints throughout the atmosphere.

Light wind- When the wind is light, the air near the surface will not mix as much. Since the ground surface is the source of the cooling, air temperature will be colder close to the surface. When the wind is very light there will be less mixing with warmer air aloft. This is especially true if the winds aloft are light also. When winds are very light a shallow layer of cold air will develop just above the ground surface. It is ideal to have a calm wind all night.