Temperature Advection


Have you ever heard your shift manager say, “Look at all this WAD” or “we have some serious CAD happening”? Do you look at him then and laugh, thinking that he is making something up? After all, what kind of words are WAD and CAD. Well, they may just be the Holy Grail of weather forecasting, the be all and end all of what the next day’s temperature may be. OK, maybe not that crucial, but it is still helpful.

WAD and CAD are acronyms for “Warm air ADvection” and “Cold air ADvection”. Advection is a big word for moving something (like temperature or moisture) from one region to another. If you’re blowing bubbles, for example, you advect bubbles away from the wand and into the air. The bubbles move from point A to point B. The same is said in meteorology. Warm air can be transported from one place to another. Cold air advection follows the same principle. Cold air is transported or advected from one region to another.



ADVECT ME NOW

Now that we have defined temperature advection, what factors control the magnitude of the temperature advection taking place? In other words, what determines how big or how little the temperature drop (CAD) or temperature increase (WAD) is going to be? Well, the strength of the wind would have something to do with it. If the air is completely still, then a blob of cold air won’t move from point A to point B. It will just sit there, in one place. If a light wind is blowing from west to east, then that same blob of cold air will move slowly from west to east. If there is a moderate wind, then that blob of cold air will move faster from west to east. Get the picture? There is something else that determines the magnitude of temperature advection: the temperature gradient. If the temperature drops off rapidly from western Pennsylvania to eastern Pennsylvania, then there is a strong temperature gradient across the state.