A cold front is defined as the transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour.
 Symbolically, a cold front is represented by a solid line with triangles along the front pointing towards the warmer air and in the direction of movement. On colored weather maps, a cold front is drawn with a solid blue line. There is typically a noticeable temperature change from one side of a cold front to the other. In the map of surface temperatures below, the station east of the front reported a temperature of 55 degrees Fahrenheit while a short distance behind the front, the temperature decreased to 38 degrees. An abrupt temperature change over a short distance is a good indicator that a front is located somewhere in between. If colder air is replacing warmer air, then the front should be analyzed as a cold front. On the other hand, if warmer air is replacing cold air, then the front should be analyzed as a warm front. Common characteristics associated with cold fronts have been listed in the table below.
A side view of a cold front (A) and how it is represented on a weather map (B) Click on image for full size Windows to the Universe image by Lisa Gardiner
Weather Fronts Weather Earth's Atmosphere A cold front is where a cold air mass is pushing into a warmer air mass. Cold fronts can produce dramatic changes in the weather. They move fast, up to twice as fast as a warm front. Cold air is dense so it is able to quickly plow a warm air mass ahead of it. Commonly, when the cold front is passing, winds become gusty; there is a sudden drop in temperature, and heavy rain, sometimes with hail, thunder, and lightning. Lifted warm air ahead of the front produces cumulus or cumulonimbus clouds and thunderstorms. Atmospheric pressure changes from falling to rising at the front. After a cold front moves through your area you may notice that the temperature is cooler, the rain has stopped, and the cumulus clouds are replaced by stratus and stratocumulus clouds or clear skies. On weather maps, a cold front is represented by a solid blue line with filled-in triangles along it, like in the map on the left (B). The triangles are like arrowheads pointing in the direction that the front is moving. Notice on the map that temperatures at ground level are warmer in front of the front than behind it. Last modified August 12, 2009 by Lisa Gardiner.
Updated July 25, 2018 By Robert Korpella
Cold front weather is an area of transition between an approaching mass of cold air and a mass of warmer air. Weather maps generally show warm and cold fronts, with a cold front appearing as a blue line, or as a blue line with blue triangles. The approaching cold front typically moves from northwest to southeast in North America, and the air behind the front is usually colder and more dry than the air ahead of the front.
The barometer begins falling as the lower air pressure associated with a cold front approaches. A falling barometer is often seen as an indication of deteriorating weather conditions. Pressure continues to fall steadily until the cold front arrives. Once it does, the air pressure bottoms out at its lowest point relative to the particular front’s intensity, then shows a steep rise. After the cold front passes through, the barometer begins a steady increase.
Cold front temperatures can fall rapidly as the front approaches, sometimes more than 8 degrees Celsius (15 degrees Fahrenheit). As cold air sinks, it displaces warmer air near the surface and sends it aloft, which accounts for the rapid deterioration in temperature readings. After the cold front passes, air temperature continues to fall, though not as rapidly before it finally stabilizes.
The displacement of air masses also signals a change in wind direction and speed. Warmer air blowing in from the south gives way to gusty winds that shift directions as the cold front passes. Winds typically blow from a northwestly direction, or western direction on the other side of a cold front.
Warm, moisture-carrying air, rapidly lifted by the cold air behind the front, results in an unstable atmosphere around the transition area. Cumulonimbus clouds rise high into the atmosphere as the cold front arrives. Capable of reaching heights between 9,100 and 13,700 meters (30,000 and 45,000 feet), the tops of cumulonimbus clouds reach the level of the jet stream. Once there, strong winds shear off the tops of the clouds, producing an anvil shape. Once the cold front moves past, fluffy cumulus clouds develop before skies eventually begin clearing.
Most of the active weather occurs as the cold front pushes through. The cold front shoves the warmer air ahead of it upward, and as it cools the air discharges its moisture. The upheaval of warm air and the development of cumulonimbus clouds signals thunderstorms with heavy rains, and some strong cells capable of producing heavy downpours. Hail and tornadoes are also possible along the cold front. Once the front passes, the weather begins to settle. Lingering showers continue after the front moves on before a gradual clearing returns.
When large masses of warm air and cold air meet, they do not mix because of density differences. In World War I, meteorologists in the “Norwegian School of Meteorology” referred to this boundary as a “front”, a military analogy to a battle line where in this case the warm and cold air masses were “fighting” for supremacy. Fronts are usually hundreds of miles long. A cold front forms when a cold, dense air mass pushes under a warm, lighter air mass, forcing the warm air to rise. The cold air advances, replacing the warm air at the surface. Rain and even thunderstorms can form as the moisture in the warm air mass rises, cools, and condenses. With a cold frontal passage, the winds will typically shift from the south to the west or north. As the front moves through, cool, fair weather is likely to follow. The temperatures behind a cold front vary depending on the type of air mass moving in. A polar air mass will bring in cold air in the winter and cool air at other times. An Arctic air mass will be associated with bitterly cold temperatures in the winter. An air mass coming off high latitude ocean areas will be unusually cold in summer but more moderate in winter. Cold Front Cloud types associated with a Cold FrontIf the cold front is highly unstable, cumulonimbus clouds producing thunderstorms commonly form along or ahead of the front. Anvil cirrus clouds may spread a considerable distance downwind from the thunderstorms. The other cloud types associated with a cold front depend on atmospheric conditions such as air mass stability and wind shear. As the front approaches, altostratus and low-level stratocumulus with intermittent light precipitation may form if the warm airmass being displaced by the cold front is mostly stable. After the passage of the cold front, the sky usually clears as high pressure builds in behind the system, although significant amounts of cumulus or stratocumulus, often in the form of long bands called cloud streets may persist if the air mass behind the front remains humid from a source of moisture. Small and unchanging amounts of cumulus or cirrus clouds in an otherwise clear sky are usually indications of continuing fair weather as long as the barometric pressure remains comparatively high. PrecipitationThe amount of precipitation associated with a cold front depends on the amount of moisture in the air and the amount of lifting the front produces. You need both abundant moisture and strong lifting to produce significant precipitation. Sometimes bands of precipitation can occur well ahead of the front especially if the warm air mass is unstable. The cold front itself commonly brings a narrow band of precipitation that follows along the leading edge of the cold front. These bands of precipitation can be very strong and can bring severe thunderstorms, hailstorms, snow squalls, and/or tornadoes. In the spring, these cold fronts can be very strong, and can bring strong winds when the pressure gradient is higher than normal. Cold fronts sometimes come through an area with little or no precipitation. These dry cold fronts can cause wildfire control problems. Wider rain bands can occur behind some shallow cold fronts which tend to have more stratiform, and less convective, precipitation. These rainstorms sometimes bring flooding, and can move very slowly when the storm steering it is strong and embedded within a meridional flow pattern (with more pole to equator motion rather than west to east motion). If the low-level cold air behind such a front has below freezing temperatures, ice storms due to freezing rain are possible. In the winter, cold fronts can bring cold spells, and occasionally snow. In the spring or summer in temperate latitudes, hail may occasionally fall along with the rain. If moisture is not sufficient, such as when a system has previously moved across a mountain barrier, cold fronts can pass without cloudiness. Frontal snow squallsSnow-covered surfaces A cold front, can produce frontal snowsqualls—an intense frontal convective line, when temperature is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow. This type of snowsquall generally lasts less than 30 minutes at any point along its path but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front where there may be a deepening low-pressure system or a series of trough lines which act similar to a traditional cold frontal passage. In situations where squalls develop post-frontally it is not unusual to have two or three linear squall bands pass in rapid succession only separated by 25 miles (40 kilometers) with each passing the same point in roughly 30 minutes apart. In cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed "thundersnow". Depiction on weather mapsOn weather maps, the surface location of a cold front is marked with a blue line of triangles pointing in the direction of the front. A mature low pressure system showing a warm front ahead of the warm mid latitude air mass streaming towards the Pole where it meets the cold polar air mass Related Articles
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What weather conditions are associated with a cold front?
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