Say what?! Cold air advection and how it affects Tennessee Valley Weather

The Weather Authority
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Data pix.

This morning I said a phrase on air that is usually limited to highly technical forecast discussions and meteorology classrooms.

That's right: I said "cold air advection".

The word "advection" describes the transport of a property from one particular spot to another. In this case, the word "property" refers to the property of matter, whether it is hot or cold, wet or dry, etc. In particular, I was referring to the atmosphere and its transport of colder air from the Midwest to the Southeast this morning -- hence, the cold air advection into the Tennessee Valley.

Surface temperatures Monday morning.
Surface temperatures Monday morning. The blue line with triangles is the cold front.

Note the sharp boundary between the warmer air to the southeast and the colder air to the northwest. Along the leading edge of this boundary is the cold front, which delineates the cold air mass from the warm air mass.

When you see a cold front on a weather map, the front is a symbol that lets you know that colder air is moving in behind the front. That cold air is advecting, or being transported, from one area of the country to the other. You can feel this on your skin, as the wind carries the colder air from west to east. You will also notice the cold air advection when temperatures drop both in distance (ie, 30s in the Midwest to 40s in the Southeast) as well as time (ie, when temperatures drop every hour, even though it is the time of day when temperatures should be rising).

Air advection is not limited to just cold air. Here in the Tennessee Valley, we experience all kinds of advection: moisture advection (when the air goes from feeling really dry to really humid); dry air advection (which is the opposite of moisture advection); and warm air advection (when the air goes from feeling really cold to really warm, and it is the opposite of cold air advection).  Often, the type of air advection that is presently occurring will give meteorologists a clue as to what to expect in the near future (ie, the next few hours to the next few days).

Mathematical equation for advection

As scientists, meteorologists take advanced math and science classes in order to earn our degrees. Within meteorology classes, we learn the equation for advection, which is depicted below by the American Meteorological Society's Glossary of Meteorology. Through this equation, we can quantify how strong -- or weak -- the type of air advection is occurring in the atmosphere.

Equation for advection. Source: American Meteorological Society
Equation for advection. Source: American Meteorological Society

Kind of puts a new perspective on weather forecasts, right?! Imagine solving this equation! After learning the math behind the process of advection, I can now "visualize" what is happening when I look at a surface temperature and pressure map: Where temperatures are rising/falling and the winds are flowing perpendicular to those temperature changes, that is where either warm/cold air advection will take place.

I hope you enjoyed this glimpse into "Meteorology 401". Feel free to reach out if you have any questions about the weather!

– Christina Edwards

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