The boundary between two air masses is known as a front, commonly observed in weather forecasts. For example, a severe cold front may drop temperatures by hundreds of degrees in minutes, and the difference between the two areas can be minor or spectacular.
Cold fronts mix cooler, drier air with warmer, more humid air, resulting in powder days. Usually, they’re blue farmers with triangle flags pointing forward in the direction of progress. When warmer, moist air collides with colder, drier air at the front edge of a storm, warm fronts emerge. A red line usually identifies them with semicircles pointing in the direction of the fronds, and they’re sometimes accompanied by severe weather.
The border between colder and warmer air masses that aren’t traveling in the same direction is marked by a stationary front. These are represented by alternating flags and semicircles (in the same colors as the above) pointing toward their respective air masses.
Occluded fronts are shown in purple on weather maps. An occlusion happens when cold air replaces warm air in the center of a low-pressure storm, pinching a region of warm air above the earth’s surface.
The confluence of a cold front, a warm front, and an occluded front, known as a “triple point,” can occasionally be the focal point for severe thunderstorms, which can ruin an afternoon run.
Only the southern plains have dry lines, which appear on surface maps as beige lines with hollow semicircles pointing in the direction of movement. They serve as a barrier between the humid air from the Gulf of Mexico and the extremely dry air from the desert west. A dryline moves eastward in huge jumps during the afternoon as a result of midday temperature. Across the spring, these fronts have the potential to cause catastrophic tornado outbreaks in Texas and Oklahoma.