A stationary front is the boundary between two air masses that is neither advancing nor retreating significantly. On weather maps, it is drawn as alternating red semicircles (pointing toward the cold air) and blue triangles (pointing toward the warm air) along the same line. Stationary fronts can persist for days in the same location when the opposing air masses are in approximate equilibrium.
Weather along a stationary front is typically prolonged and persistent: extended periods of cloud, intermittent rain or drizzle, and sometimes fog, as warm air rides gently up and over the cold air boundary (similar to a slow-moving warm front). The precipitation tends to be lighter than at active fronts but covers wider areas and lasts longer, leading to significant accumulated rainfall and potential flooding — especially in mountainous terrain where orographic enhancement amplifies totals.
Stationary fronts are important in meteorological analysis because they can reactivate when the balance shifts: if cold air pushes forward, the front becomes a cold front; if warm air advances, it becomes a warm front. Small waves (undulations) can develop along stationary fronts, sometimes growing into new depressions. In summer, stationary fronts draped across Europe can focus persistent thunderstorm activity along the boundary for days. The Mei-yu front in East Asia is a famous semi-permanent stationary front responsible for the "plum rain" season in China and Japan.