Stationary front

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).

Stationary front symbol: solid line of alternating blue spikes pointing to the warmer air mass and red domes pointing to the colder air mass

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 also 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, 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

Although the stationary front's position may not move, there is air motion as warm air rises up and over the cold air, responsive to the geostrophic induced by frontogenesis. A wide variety of weather may occur along a stationary front. If one or both air masses are humid enough, cloudy skies and prolonged precipitation are recurring, with storm trains or mesocyclone systems. When the warmer air mass is very moist, heavy or extreme rain or snow can occur.

Stationary fronts may dissipate after several days or devolve into shear lines. A stationary front becomes a shear line when air density contrast across the front vanishes, usually because of temperature equalization, while the narrow wind shift zone persists for some time. That is most common over open oceans, where the ocean surface temperature is similar on both sides of the front and modifies both air masses to correspond to its temperature. That sometimes also provides enough heat energy and moisture to form subtropical storms and tropical cyclones at the surface.

Warm front

Warm fronts 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. Sleet forms when a warm front meets an extremely cold air mass.

Cold front

Cold fronts, 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). Cold fronts can cause rapid changes in weather. When a cold front moves into an area, it brings with it a drop in temperatures, which can lead to thunderstorms. These can cause big changes in the weather.

History context

Stationary front may affects the environment and causes disasters.

April 21, 1885 – Barber County Flood: The event cause by stationary front because of Blocking High-Pressure Systems. Stationary fronts act as a barrier between cold Arctic air masses and relatively warm southern air, trapping cold air masses in the region for long periods of time. This led to intense rainfall along the Elm Creek and Medicine River, resulting in the flood that killed at least 19 people.

January 31- February 12, 1899 – Prolonged Arctic Outbreak: An arctic outbreak moved into western Kansas. From January 31st until February 12th, the temperature did not rise above 20 degrees at Dodge City. Stationary front cause the event by resulting Cold Air Entrapment. The stationary front acted as a barrier, trapping the Arctic air mass over the region. The front essentially kept the cold temperatures in place by allowing warm air to take its place. This resulted in a prolonged period of cold weather with temperatures not rising above 20 degrees in nearly two weeks.

May 22, 1951 – Hays Flood: Extremely heavy rains (including eleven inches of rain in just two hours!) from late night of May 21 into the early morning hours of May 22 produced one of the worst flooding disasters in the history of Hays. Stationary front cause the Moisture Convergence that cause the flood. A stationary front can act as a boundary where warm, moist air on one side converges with cooler, denser air on the other side. resulting in an increase in humidity and often leading to cloud formation and precipitation. In May 1951, moisture-laden air can converge along a stationary front, causing flooding.

External links

• Quasi-Stationary Front (also known as Stationary Front).
• Stationary Front.