How do stationary fronts form

At upper levels, the front is typically parallel to the prevailing flow. A stationary front usually remains in the same area for hours to days, and may undulate as atmospheric short waves move eastward along the front. Although the stationary front's position may not move, there is air motion as warm air rises up and over the cold air, as a response to the ageostrophy 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 can occur, with mesocyclone systems. When a cold air mass takes the place of a warm air mass, there is a cold front. Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease.

If the humidity is high enough, some types of cumulus clouds will grow. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain showers, snow showers, or thunderstorms with blustery winds.

A squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass. This mass is drier so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Along a warm front , a warm air mass slides over a cold air mass. When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable.

Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. The weather ahead of the cold occlusion is similar to that of a warm front while that along and behind the cold occlusion is similar to that of a cold front.

Fronts are zones of transition between two different air masses. Figure 1 - Types of Fronts. Fronts are boundaries between air masses of different temperatures.

The type of front depends on both the direction in which the air mass is moving and the characteristics of the air mass. To locate a front on a surface map, look for the following: sharp temperature changes over relatively short distances, changes in the moisture content of the air dew point , shifts in wind direction, low pressure troughs and pressure changes, and clouds and precipitation patterns.

Cold front- a front in which cold air is replacing warm air at the surface. Some of the characteristics of cold fronts include the following: The slope of a typical cold front is vertical to horizontal. Cold fronts tend to move faster than all other types of fronts. Cold fronts tend to be associated with the most violent weather among all types of fronts.

Cold fronts tend to move the farthest while maintaining their intensity. Cold fronts tend to be associated with cirrus well ahead of the front, strong thunderstorms along and ahead of the front, and a broad area of clouds immediately behind the front although fast moving fronts may be mostly clear behind the front. WMC -Our weather forecast has been rather unsettled and we have had this pattern before.

The culprit for the wetter pattern is a stationary front. A stationary front forms when a cold front or warm front stops moving. This occurs when two air masses are pushing against each other but neither is powerful enough to move the other. In addition of the wind is blowing parallel to the front instead of perpendicular, this can also help a front stay parked across the area.

A stationary front may stay across an area for days. If the wind direction changes the front will start moving again, becoming either a cold or warm front. Or the front may break apart altogether. Because a stationary front represents two air masses, there are often differences in air temperature and differences in wind on opposite sides of it.

The weather is often cloudy along a stationary front and rain or snow often falls, especially if the front is in an area where the pressure is low.

When you look at the weather map, a stationary front is represented as red semi-circles and blue triangles like on the map below. The blue triangles will point in one direction representative of the cold air and the warm front represented by the red semi-circles represents the warmer air.