Warm front

	Email		Print
	Bookmark		Link

Warm front

A warm front is defined as the leading edge of an advancing mass

Air mass

In meteorology, an air mass is a large volume of air that have characteristics of temperature and water vapor content. Air masses cover many hundreds or thousands of square miles, and slowly change in accordance with the surface below them....
of warm air; it separates warm air from the colder air ahead.

masses are large bodies of air with similar properties of temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
and humidity

Humidity

Humidity is the amount of water vapor in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapor in a Air parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature....
that form over source regions, and the warm air masses behind warm fronts are not only warmer but higher in humidity than the colder air preceding them.

Discussion

Ask a question about 'Warm front'

Start a new discussion about 'Warm front'

Answer questions from other users

Full Discussion Forum

Encyclopedia

A warm front is defined as the leading edge of an advancing mass

Air mass

Development of warm fronts

Air masses are large bodies of air with similar properties of temperature

Temperature

Humidity

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
, mixing between the two air masses is discouraged. Being lighter, the warm air mass is unable to displace the cooler air mass and instead is forced upward along the upper boundary of the colder air in a process known as overrunning. The boundary between the two air masses has a gradual slope of 1300 and lifting is slow but persistent.

As the air mass rises into regions of lower pressure, it expands and cools. As it cools, water vapor

Water vapor

Water vapor or water vapour , also aqueous vapor, is the gas phase of water . Water vapor is one Phase of the water cycle within the hydrosphere....
condenses

Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
and forms extensive cloud

Cloud

A cloud is a visible mass of Drop or frozen crystals floating in the Celestial body atmosphere above the surface of the Earth or another planetary body....
coverage. The first clouds to form along the sloping surface of the cold air are nimbostratus, followed by altostratus, cirrostratus and cirrus

Cirrus cloud

Cirrus clouds are characterized by thin, wisplike strands, often accompanied by tufts, leading to their common name of mare's tail. Sometimes these clouds are so extensive that they are virtually indistinguishable from one another, forming a sheet of cirrus called Cirrostratus cloud....
. Once the clouds have thickened to 2,500m from the earth’s surface, rain can begin to fall.

If the air mass is relatively stable, rainfall will increase until the front reaches the location, at which time the clouds can extend all the way to the earth’s surface as fog

Fog

Fog is a cloud bank that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog....
. Once the front passes, the location experiences quick warming and clearing. If the air mass is unstable, thunderstorm

Thunderstorm

File:FoggDam-NT.jpgA thunderstorm, also known as an electrical storm or a lightning storm, is a form of weather characterized by the presence of lightning and its effect: thunder....
s may precede and follow the front.

In the northern hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of the equator?the word sphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator....
, a warm front causes a shift of wind from southeast to southwest, and in the southern hemisphere

Southern Hemisphere

The Southern Hemisphere is the half of a planet that is south of the equator?the word sphere literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator....
a shift from northeast to northwest. Common characteristics associated with warm fronts include:

Weather phenomenon	Prior to the Passing of the Front	While the Front is Passing	After the Passing of the Front
Temperature	Cool	Warming suddenly	Warmer, then leveling off
Atmospheric pressure	Decreasing steadily	Leveling off	Slight rise followed by a decrease
Winds	South to southeast (northern hemisphere) North to northeast (southern hemisphere)	Variable	South to southwest (northern hemisphere) North to northwest (southern hemisphere)
Precipitation	Showers, snow Snow Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of this precipitation is called snowfall.... , sleet Rain and snow mixed Rain and snow mixed is precipitation composed of rain and partially melted snow. This precipitation can occur where the temperature in the lower part of the atmosphere is slightly above the freezing point .... , or drizzle Rain Rain is liquid precipitation . On Earth, it is the condensation of atmospheric water vapor into droplet heavy enough to fall, often making it to the surface....	Light drizzle	Usually none, sometimes light rain or showers
Clouds	Cirrus Cirrus Cirrus can refer to:Cirrus cloud, a type of cloudIn biology, a bundle of cilium fused together into a large mobile projectionChrysler Cirrus, a car produced by DaimlerChrysler... , cirrostratus, altostratus, nimbostratus, then stratus Stratus Stratus* may refer to:Stratus cloud, a cloud typeNimbostratus cloud, a cloud typeStratocumulus cloud, a cloud typeAltostratus cloud, a cloud type... and fog Fog Fog* is a cloud bank that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog.... ; occasionally cumulonimbus in summer	Stratus Stratus Stratus may refer to:Stratus cloud, a cloud typeNimbostratus cloud, a cloud typeStratocumulus cloud, a cloud type*Altostratus cloud, a cloud type... , sometimes cumulonimbus	Clearing with scattered stratus Stratus Stratus may refer to:Stratus cloud, a cloud typeNimbostratus cloud, a cloud typeStratocumulus cloud, a cloud type*Altostratus cloud, a cloud type... , sometimes scattered cumulonimbus
Visibility	Poor	Poor, but improving	Fair in haze
Dew Dew Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by thermal radiation its heat, atmospheric moisture condensation at a rate greater than that at which it can evaporation, resulting in the formation of water droplets.... Point	Steady rise	Steady	Rise, then steady

On weather map

Weather map

A weather map is a tool used to display information quickly, showing the analysis of various meteorological quantities at various levels of the atmosphere....
s, the surface location of a warm front is marked with a red line of half circles pointing in the direction of travel. On colored weather maps, warm fronts are illustrated with a solid red line.

Warm front

Development of warm fronts

See also

External links