Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing (at ground level) a warmer mass of air.
Development of cold front
The cooler, denser air wedges under the less dense warmer air, lifting it, which can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. This upward motion causes lowered pressure along the cold front. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel. A cold front's location is at the leading edge of the temperature drop off, which in an isotherm analysis would show up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts can move up to twice as fast and produce sharper changes in weather than warm fronts. Since cold air is denser than warm air, it rapidly replaces the warm air preceding the boundary. Cold fronts are usually associated with an area of low pressure.
In the northern hemisphere, a cold front usually causes a shift of wind from southeast to northwest, and in the southern hemisphere a shift from northeast to southwest. Common characteristics associated with cold fronts include:
| Weather phenomenon | Prior to the Passing of the Front | While the Front is Passing | After the Passing of the Front |
|---|---|---|---|
| Temperature | Warm | Cooling suddenly | Steadily cooling |
| Atmospheric pressure | Decreasing steadily | Lowest, then sudden increase | Increasing steadily |
| Winds |
|
Gusty; shifting |
|
| Precipitation/conditions* | Brief showers | Thunderstorms, sometimes severe | Showers, followed by clearing |
| Clouds* | Increasing: Cirrus, cirrostratus, and cumulonimbus | Cumulonimbus | Cumulus |
| Visibility* | Fair to poor in haze | Poor, but improving | Good, except in showers |
| Dew Point | High; steady | Sudden drop | Falling |
- Provided there is sufficient moisture.
Definition: A boundary between 2 air masses, 1 cold and the other warm
Precipitation
A cold front commonly brings a narrow band of precipitation that follows along the leading edge of the cold front. These bands of precipitation are often very strong in nature, and especially in the Spring and Summer months, can bring severe thunderstorms and/or tornadoes. In the spring, these cold fronts can be very strong, and can bring strong winds when the pressure gradient is tighter than normal. In the summer, cold fronts can cause severe thunderstorms and hailstorms, but in the winter, cold fronts sometimes come through an area with little or no precipitation. In the autumn months, cold fronts rarely bring severe thunderstorms, but are known for bringing heavy, and widespread rainstorms. These rainstorms sometimes bring flooding, and can move very slowly because cold fronts are more prone to slow movement in the fall. In the winter, cold fronts can bring severe cold spells, and heavy snowstorms. If moisture is not sufficient, cold fronts can pass without producing any precipitation at all, and the skies could be cloudless. Cold fronts do not produce the moisture, it will just condense against the cold air into cloud and rain droplets if there is enough water vapor in either airmass. Because the cold air wedges under the warm air, it forces it to rise, creating instability. If moisture is sufficient, it will condense, creating storms, clouds, and/or rain....
Temperature changes
Cold fronts are the leading edge of a frigid air mass, hence the name "cold front". They can bring several cold spells in the fall (autumn) and winter. Very often, cold fronts are associated with deadly cold weather. Sometimes, though, cold fronts have no significant effect on the weather. The cold fronts in the late fall become more polar in nature, and tend to bring very cold weather, and temperature drops by up to 30°F. When cold fronts come through, there is usually a quick, yet strong gust of wind, that shows that the cold front is passing. The effects from a cold front can last only a few hours to several weeks, depending on when the next weather front comes through.The air behind the front is cooler than the air it is replacing. the warm air is forced to rise so it cools. as the cooler air can not hold as much moisture as warm air, clouds form and rain occurs.
Association with warm fronts
Cold fronts are very often associated with a warm front, squall line, or other weather front. Very commonly, cold fronts have an adjacent warm front that is ahead of the cold front. This is known as an occluded front. This forms an area where warm air is occurring and interacting with the cold front. In this area known as a warm sector. In the warm sector, very often severe thunderstorms, tornadoes, and hailstorms occur, because of the sharp difference between the warm air that is associated with the warm front, and the cold air that is associated with the cold front. A cold front is considered a warm front if it retreats, and called a stationary front if it stalls.
Formation
Cold fronts form when a cooler air mass moves into an area of warmer air. The warmer air interacts with the cooler air mass along the boundary, and usually produces precipitation.