Warm front

warm sectorwarmGulf moisturemoistureWarm air fronts
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient.wikipedia
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Weather front

frontal systemfrontal boundaryfront
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient.
Warm fronts are usually preceded by stratiform precipitation and fog.

Fog

advection fogfreezing fogground fog
Fog can also occur preceding a warm frontal passage. 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.
It is common as a warm front passes over an area with significant snow-pack.

Cold front

cold frontsArctic blastcold
Warm fronts lie within broader troughs of low pressure than cold fronts, and move more slowly than the cold fronts which usually follow because cold air is denser and less easy to remove from the Earth's surface.
Cold fronts move faster than warm fronts and can produce sharper changes in weather.

Cloud

cloudscloud formationcloudy
As it cools, any water vapor that is present will condense and form extensive cloud cover.
Warm fronts associated with extratropical cyclones tend to generate mostly cirriform and stratiform clouds over a wide area unless the approaching warm airmass is unstable, in which case cumulus congestus or cumulonimbus clouds are usually embedded in the main precipitating cloud layer.

Air mass

air massesair streamMaritime Tropical air masses
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. If the air mass is unstable, thunderstorms may precede and follow the front and temperature changes will be larger.
Warm fronts are usually preceded by stratiform precipitation and fog.

Surface weather analysis

cold frontsurface analysissurface
On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.
Warm fronts mark the position on the Earth's surface where a relatively warm body of air has displaced colder air.

Rain

rainfallrainwaterrainstorm
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.
Stratiform (a broad shield of precipitation with a relatively similar intensity) and dynamic precipitation (convective precipitation which is showery in nature with large changes in intensity over short distances) occur as a consequence of slow ascent of air in synoptic systems (on the order of cm/s), such as in the vicinity of cold fronts and near and poleward of surface warm fronts.

Cirrus cloud

cirruscirrus cloudsCirriform
The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first, changing to cirrostratus as the front approaches.
These conditions commonly occur at the leading edge of a warm front.

Nimbostratus cloud

nimbostratusNimbusnimbus cloud
Once the clouds have thickened to 2500 m from the earth’s surface, precipitation can begin to fall from heavy nimbostratus.
Nimbostratus occurs along a warm front or occluded front where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher-level clouds such as cirrostratus and altostratus.

Cirrostratus cloud

cirrostratuscirrostratus cloudsCs
The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first, changing to cirrostratus as the front approaches.
Cirrostratus clouds sometimes signal the approach of a warm front if they form after cirrus and spread from one area across the sky, and thus may be signs that precipitation might follow in the next 12 to 24 hours or as soon as 6–8 hours if the front is fast moving.

Stratocumulus cloud

stratocumulusScstratocumulus castellanus
Cloud types can be mixed, but usually consist of stratocumulus, which can range to being broken to covering the entire sky depending on distance from the centre of low pressure.
'Dull weather' is a common expression incorporated with overcast stratocumulus days, which usually occur either in a warm sector between a warm and cold front in a depression, or in an area of high pressure, in the latter case, sometimes persisting over a specific area for several days.

Occluded front

occludedtrowaloccluded low
In meteorology, an occluded front is a weather front formed during the process of cyclogenesis, when a cold front overtakes a warm front.

Stratus cloud

stratusstratiformstratus clouds
Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches.

Temperature

temperaturesair temperaturewarm
Air masses are large bodies of air with similar properties of temperature and humidity that form over source regions.

Humidity

humidspecific humidityabsolute humidity
Air masses are large bodies of air with similar properties of temperature and humidity that form over source regions.

Density

densemass densitydensities
Because of a warm air mass’s higher temperature and thus lesser density, mixing between the two air masses is unlikely.

Water vapor

water vapourvaporevaporation
As it cools, any water vapor that is present will condense and form extensive cloud cover.

Condensation

condensecondensedcondenses
As it cools, any water vapor that is present will condense and form extensive cloud cover.

Thunderstorm

thunderstormssevere thunderstormelectrical storm
If the air mass is unstable, thunderstorms may precede and follow the front and temperature changes will be larger.

Northern Hemisphere

NorthernNorth HemisphereNorthern Hemispheric
In the northern hemisphere, a warm front causes a shift of wind blowing from southeast to southwest, and in the southern hemisphere a shift from winds blowing from northeast to northwest.

Wind

windsgustsgust
In the northern hemisphere, a warm front causes a shift of wind blowing from southeast to southwest, and in the southern hemisphere a shift from winds blowing from northeast to northwest.

Southern Hemisphere

SouthernaustralS. Hemisphere
In the northern hemisphere, a warm front causes a shift of wind blowing from southeast to southwest, and in the southern hemisphere a shift from winds blowing from northeast to northwest.

Altostratus cloud

altostratusaltostratus,
A thickening and lowering of these high clouds into middle-étage altostratus or altocumulus is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours.

Cirrocumulus cloud

cirrocumulusCc
However, if cirrocumulus also appears, there is greater airmass instability approaching ahead of the front.