I am sure you have heard our Chief Meteorologist Dan Skoff mention the term compressional warming whenever a powerful cold front is headed our way. It is the reason why the temperatures often heat up quite a bit the day before the front rolls into town. In this edition of Weather Word of the Week we are going to explore this important topic.
What is it?
Compressional warming is exactly what it sounds like, warming the air by compressing or squeezing it. The molecules of the air mass get pressed together increasing the friction which in return increases the temperature.
Imagine a bike pump. Have you ever noticed that after pumping your bike tires up that the hose of the pump gets pretty warm? This is because as you push the pump down you are pressing the air molecules against each other. As mentioned above this increases the friction of the air molecules which in return produces heat as a by-product.
Physically this is a direct application of Newton’s First Law of Thermodynamics.
Now let’s apply this same concept to the atmosphere!
Compressional Warming Along a Cold Front
As discussed in a previous episode of Weather 101 a cold front has a sloped surface along its leading edge. To learn more about cold fronts click HERE.
The steepness of a cold front’s slope depends on the strength of the cold air mass behind it. The steeper the slope the greater the amount of compressional warming ahead of it. This means that the stronger the cold front moving into town, the greater the temperature will rise ahead of it.
Another factor affecting the amount of compressional warming is the timing of the frontal passage. If the front pushed through overnight into the morning, the warming will be significantly less compared to an afternoon frontal passage. The afternoon allows the daily solar heating to combine with the compressional warming thereby increasing the air temperature quite a bit more.
Example of Compressional Warming Locally
Notice how warm the temperatures were before the cold front pushed through! Upper 70s to mid 70s across the region. That is quite the warm up from temperatures early that morning.
The temperatures behind the cold front dropped dramatically. Some places saw a 20 degree change in a few hours. This is proof that the cold front was pretty strong.
Check out the animation of the temperature rise and fall associated with the cold front below!
Next time your Weather Authority team mentions the advancement of a strong cold front, watch for the temperatures to increase ahead of the frontal passage. This is the process of compressional warming in action!