Brrrrrrrr! Wednesday & Thursday mornings’ temperatures sure had you reaching for the jacket before you left for the morning commute and drive to school.
The official low in San Antonio dropped to 46? on Wednesday, making it the coldest morning that the Alamo City had experienced since April 8… that was more than 190 days ago!
Thursday morning was a touch warmer by a few degrees but still chilly, with the official thermometer over at San Antonio International Airport dropping to 50?.
There are a few different factors that made for the chilly starts found these past few mornings: cooler and drier air that arrived behind Sunday night’s cold front, but also clear skies.
Those clear skies allow for an additional overnight cooling process to occur, which we call radiational cooling. More on that below!
To understand this process that happens overnight, we first have to talk about what happens during the day.
Each day, the Earth receives heat from the sun in the form of solar radiation, which in turn warms up our temperatures at the surface.
Some of that heat then escapes back to space through the overnight hours when we are not receiving solar radiation, which is the process of radiational cooling.
This process is more efficient when we have clear skies in place (like Tuesday and Wednesday night!) and calm winds, since that heat is able to escape back to space more easily.
When there are clouds in place, they can act as a blanket to some of that heat trying to escape and trap it near the ground.
This often ends up holding our temperatures at the surface a little warmer overnight than what they would be if skies were clear.
Pretty cool stuff, right?!
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