Cold air advection and its counterpart warm air advection (both processes called thermal advection together) is one of the most fundamental aspects of analyzing and forecasting the weather by using analysis charts and model images. Cold air advection is the horizontal transport of colder air into a point location. The most common place this occurs is behind a cold front. Cold air advection is best analyzed above the friction layer. Near the surface there are numerous contaminating influences to the thermal advection process such as warming from the earth’s surface, evaporation, wind direction shifts, vertical mixing of air and solar heating transport. Thus, the 850 level is great to use for locations near sea level and 700 mb is great to use for locations at higher elevations when analyzing thermal advection. When cold air advection occurs, colder air will replace warmer air. This decreasing temperature change must occur due to a horizontal transport of air in order to be cold air advection. Processes such as evaporative cooling, adiabatic cooling and radiative cooling are not cold air advection. The diagram below shows the temperature contrast ahead and behind a cold front. In this case, the region that will experience the cold front will also experience cold air advection.  When using charts and models, weather analyzers and forecasters note the arrangement of 3 features which are height contours, isotherms, and the angle of intersection between height contours and isotherms. The diagram below has the definitions of several of these terms. The next diagram depicts an example of the cold air advection process. To maximize cold air advection it helps to have closely spaced height contours (indicates faster wind), closely spaced isotherms (indicates temperature will decrease more quickly as colder air moves in) and height contours and isotherms that are perpendicular to each other (maximizes transport of colder air into a fixed point). To reduce cold air advection it helps to have widely spaced height contours (indicates slower wind), wider spaced isotherms (indicates temperature will decrease slower as colder air moves in) and height contours and isotherms that are parallel to each other (minimizes transport of colder air into a fixed point).   Cold air advection can have the following influences on weather: 1. Cold air advection often brings in drier air 2. Cold air advection is a sinking process thus this can reduce precipitation chances and precipitation amounts 3. Weather will often be cooler than normal 4. It can indicate a big change in the weather, especially when significant |