Coldfront

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For the Star Trek: Enterprise episode, see Cold Front (Enterprise).

The symbol of a cold front: a blue line with triangles pointing in the direction of travel

A cold front defined as the leading edge of a cooler and drier mass of air. The air with greater density 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, and sometimes, a warm front.

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	Southwest to southeast (northern hemisphere) Northwest to northeast (southern hemisphere)	Gusty; shifting	North to west (usually northwest) (northern hemisphere) South to west (usually southwest) (southern hemisphere)
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

1 Precipitation
2 Temperature changes
3 Association with warm fronts
4 Formation
5 See also
6 References
7 External links

Precipitation

Illustration of a cold front

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, and with little or no effect on temperature. 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.

Association with warm fronts

Occluded cyclone example. The triple point is the intersection of the cold, warm, and occluded 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 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.