Weather map showing a stationary front
Windows to the Universe image by Lisa Gardiner
A stationary front typically forms from either a cold or warm front that has stopped moving. This happens when two air masses are pushing against each other but neither is powerful enough to move the other. Winds, which often help move fronts, blowing parallel to the front instead of perpendicular can help the front stay in place.
A stationary front may stay put for days. If the wind direction changes, blowing perpendicular, the front will start moving again, becoming either a cold front or a warm front, or the front may dissipate.
Because a stationary front marks the boundary between two different air masses, there are often differences in air temperature and wind on opposite sides of a front. The weather is often cloudy along a stationary front and rain or snow commonly falls, especially if the front is in an area of low atmospheric pressure.
On a weather map, a stationary front is shown as alternating red semicircles and blue triangles like in the map at the left. The blue triangles point in one direction and the red semicircles point in the opposite direction.
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