WX MODEL 9: Cold Air Progression


The movement of shallow cold air is going to depend on several factors. One factor is the forcing producing by the cold air. This can be analyzed by examining the wind speed within the cold air. Faster wind will help progress the cold air. Another factor is the elevation change encountered by the cold air. Cold air is dense and will thus more easily flow downhill than it will uphill. If there are mountain barriers then the cold air will not go over the mountains unless the cold air is deep or has significant forcing within it (strong wind speeds). Situations in which shallow cold air will not go over a topographic barrier are termed cold air damming. Another factor is the depth of the cold air. Deeper cold air will more easily go over topographic barriers as compared to very shallow cold air.

The image below is that of shallow cold air moving toward the south. Notice over Colorado the forcing of the air is weak. The increasing elevations and mountains are one barrier to the cold air moving in. Another barrier is weak wind pushing the cold air toward the west. This can cause, such as in this case, cool temperatures in eastern Colorado but warmer temperatures in western Colorado.