fronts

Fronts are boundaries that separate two air masses of different temperature, humidity, and density. In meteorology, a front is the surface where air masses meet and where associated weather changes occur as the air masses interact. The term also appears in military and geopolitical contexts to describe the area where opposing forces are engaged, or the line of operations.

In weather, fronts form in regions where large-scale air masses with contrasting characteristics converge, commonly on the edges of mid-latitude cyclones. Four main types are recognized: cold fronts, warm fronts, stationary fronts, and occluded fronts. A cold front involves cold air displacing warmer air, often with a steep boundary and convective showers or thunderstorms, followed by cooler, drier air. A warm front forms when warm air glides over a retreating cold air mass, typically bringing widespread, steady precipitation and layered clouds. A stationary front has little movement between the air masses, causing prolonged, often mixed and light precipitation. An occluded front occurs when a cold front overtakes a warm front, lifting the warm air aloft and producing complex weather patterns.

Fronts are key features in weather forecasting. Their movement, strength, and interaction with topography and atmospheric moisture determine precipitation timing, intensity, and type. Weather maps depict fronts with lines and symbols indicating the type, direction of movement, and changes in temperature and pressure.

In military usage, a front denotes the recognized boundary where active combat operations occur or are planned, such as a front line or battlefront; it may shift as operations progress.