Why You Still Get Light Winds on a Calm Fall or Winter Day (Imagery credit: NCAR/UCAR)

DISCUSSION: As we head deeper into Fall and towards the beginning of Winter 2018-2019, there are several curious things which people wonder about day-to-day weather on even the calmest of days. More specifically, om days when there is little to no active weather occurring in a given region, there are still many curious things which will often occur even on the clearest of days. One such example of an unusual phenomena to the minds of most average people is when there is a random, light breeze on a calm, clear day with no clouds or precipitation in sight. However, there happens to be a clear and concise explanation for why such breezes occur on the calmest of days.
 
First off, it is important to understand that when infrared radiation enters the Earth’s atmosphere and reaches all the way to the surface of the Earth, this process acts to heat the immediate surface and surface layer. Thus, this incoming infrared radiation which reaches the surface of the Earth acts to increase the Earth’s skin temperature and gradually will partially be re-emitted back from the immediate surface and surface-based layer of the Earth in the form of weak low-level thermals. Thermals are effectively small-scale perturbations (i.e., smaller-scale changes) which transfer infrared radiation-based heat energy just above the surface. As a result of this infrared radiation being re-emitted from the surface of the Earth, these low-level thermals act to induce very small-scale pressure changes. These very small-scale pressure changes ultimately lead to light breezes which will occasionally reach the surface of the Earth.
 
Therefore, the next time that you go outside on a calm Fall or Winter day, you can now understand how and why you will sometimes experience an occasional light breeze even on the calmest of days. Of course, it is worth noting that such light breezes occur even more often on Summer days since there is even more intense infrared radiation reaching the surface of the Earth due to a higher Sun angle during the Summer-time months.
 
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© 2018 Meteorologist Jordan Rabinowitz