thumb|right|Stationary front symbol: solid line of alternating blue spikes pointing to the warmer air mass and red domes pointing to the colder air mass
thumb
A stationary front (or quasi-stationary front) is a weather front or transition zone between two air masses when each air mass is advancing into the other at speeds less than 5 knots (about 6 miles per hour or about 9 kilometers per hour) at the ground surface. These fronts are typically depicted on weather maps as a solid line with alternating blue spikes (pointing toward the warmer air) and red domes (facing the colder air).
Development
A stationary front may form when a cold or warm front slows down or grows over time from underlying surface temperature differences, like a coastal front. Winds on the cold air and warm air sides often flow nearly parallel to the stationary front, often in opposite directions along either side of the stationary front. A stationary front usually remains in the same area for hours to days and may undulate as atmospheric waves move eastward along the front.
Stationary fronts may change into a cold or warm front, and may form one or more extratropical or mid-latitude cyclones at the surface when atmospheric waves aloft are fiercer, or when cold or warm air masses advance fast enough into other air masses at the surface. For instance, when a cold air mass traverses sufficiently quick into a warm air mass, the stationary front changes into a cold front.
There are frequently variations in wind and air temperature on opposing sides of a stationary front because it delineates the boundary between two air masses. Along a stationary front, the weather is typically overcast with rain or snow, particularly if the front is in an area of low air pressure.
Characteristics
A warm front is a slow-moving air mass that displaces a cold air mass. Warm fronts typically move at speeds of 10 to 25 miles per hour, and clouds form as warm air is lifted up, then cooled and condensed to form clouds. A warm front may bring persistent precipitation, fog, and cloudy skies, signaling the start of wet weather. Sleet can also form when a warm front meets an extremely cold air mass, cooling the air below. On the other hand, cold fronts move faster than warm fronts, at speeds of 25 to 30 miles per hour (up to 60 miles per hour).