During World War I, Norwegian meteorologists visualized these zones of air mass interactions as analogous to battle lines and tagged them “fronts,” as in battlefronts.…density differences are most often caused by temperature differences ….before going to depth we should acknowledge the role of air masses and a little familiarize with types of air masses.
Generally we assume fronts on a surface weather map just have a horizontal extension but this is not true fronts have horizontal extension as well as vertical extension. Figure illustrates the vertical extent of two frontal zones — the polar front and the arctic front. The polar front boundary, which extends upward to over 5 km, separates warm, humid air to the south from cold polar air to the north. The arctic front, which separates cold air from extremely cold arctic air,
surface weather map illustrating four different fronts.As we move from west to east across the map, the fronts appear in the following order: a stationary front between points A and B; a cold front between points B and C; a warm front between points C and D; and an occluded front between points C and L.A surface weather map showing surface-pressure systems, air masses, fronts, and isobars (in millibars) as solid gray lines. Large arrows in color show air flow. (Green-shaded area represents rain; pink-shaded area represents freezing rain and sleet; white-shaded area represents snow.)
Notice the point A and B in both figures in 2 D view warm sir replaces the cold air but in 3D view actually the warm air is rising over the wedge of cool air and here and advancing continental polar air replaces the mt air but in 3d view mt air glides over the advancing cp air
that enters the United States. from the Gulf of Mexico and ………….. This means that if you traveled 200 kilometers (120 miles) ahead of the surface location of a warm front, the frontal surface would be 1 kilometer. Warm air ascends on the retreating wedge of cold air it expands and cools adiabatically. As a results moisture in the ascending air condenses to generate clouds that may produce precipitation.
The first sign of approaching a warm front is cirrus cloud that is 1000 km or more ahead of the surface front. As the front nears, cirrus clouds grade into cirrostratus that gradually blend into denser sheets of altostratus. About 300 kilometers (180 miles) ahead of the front, thicker stratus and nimbostratus clouds appear and precipitation often commences. During the hot summer months when moist conditionally unstable air is often forced aloft, towering cumulonimbus clouds and thunderstorms may occur
We identify a warm front from its weather elements and before passage, during passage and after passage conditions. Frontal weather also associated with these weather elements.
we can see a large contrast in air temperature and dew point on either side of the front. Since the cold front is a trough of low pressure so when we moves towards a cold front then pressure increasing towards frontal position and when we moves away from front pressure starts decreasing. One important fact to remember is that the lowest pressure usually occurs just as the front passes a station. Notice that, as you move toward the front, the pressure drops, and, as you move away from it, the pressure rises. This is Doppler radar image the image illustrates the precipitation pattern along the front Notice that light-to-moderate rain (color green) occurs over a wide area along the front, while the heavier precipitation (color yellow) tends to occur in a narrow band along the front itself. Thunderstorms (color red) do not occur everywhere,but only in certain areas along the front.
Here the cold front catches up the warm front and partially occluded front forms. Finally the warm front overrides on cold front and a occluded front forms.
the air that had been behind the cold front is colder than the cool air it is overtaking. In the first step a clod front advancing towards a warm front and in second step the cold front catches up the warm front but the cold air of warm front is warmer then the air behind a cold front that’s why the warm front rises over the cold front….
It is also possible for the air behind an advancing cold front to be warmer than the cold air it is overtaking.. These warm-type occluded fronts (Figure 9–9b) frequently occur along the Pacific Coast, where milder maritime polar air invades more frigid polar air that had its origin over the continent.
Presented to: Mr. Shaukat Ali Awan
Fronts, Formation, Identification and
Department of Space Science ,University of the Punjab, Lahore
Fronts are boundary surfaces that separate air masses of different densities one of
which is usually warmer and contains more moisture than the other.
The zones that Separate the vast sizes of air masses.
A front is the transition zone between two air masses of different densities.
Separate air masses with contrasting temperatures. Often, they separate air masse
s with different humidity's as well called Fronts.
Fronts can form between any two contrasting air masses.
An air mass as the term implies is an immense body of air usually 1600 km whic
h is characterized by homogeneous physical properties in particular
temperature and moisture content at any given altitude.
Frontal Surface or Frontal Zone
The upward extension of a front is referred to as a frontal surface or front
Formation of Fronts
Generally, the air mass located on one side of a front moves faster than
the air mass on the other side. Thus, one air mass actively advances into
the region occupied by another and collides with it.
As one air mass moves into the region occupied by another, minimal
mixing occurs along the frontal surface.
Instead the air masses retain their identity as one is displaced upward
over the other. No matter which air mass is advancing, it is always the
warmer less dense air that is forced aloft.
Whereas the cooler, denser air acts as a wedge on which lifting occurs.
The term overrunning is applied to the process of warm air gliding up over a col
d air mass.
When the surface position of a fr
ont moves so that warmer air in
vades territory formerly occupie
d by cooler air, it is
called a warm front.
Warm fronts are usually as
sociated with maritime tropi
cal (mT) air “glides” over cooler
air positioned over land.
The boundaries separating th
ese air masses have very
gradual slopes that average ab
This rising of warm air over
cold, called overrunning
A temperature inversion called a frontal inversion exists in the region of the uppe
r level front at the boundary where the warm air overrides the cold air.
Frontal Inversion in Warm Front
Identification and Frontal Weather
Before Passage During
Temperature Cool or Cold Rising Warmer
Winds East or southeast Variable South or Southwest
Precipitation Light-to-moderate rain,
snow, or freezing rain in
Heavy rain possible in
Clouds Cirrus, cirrostratus,
air is Conditionally
Pressure Falling Falling
Humidity Moderate to high Rising High, particularly in
When cold air actively advances into a region occupied by warmer air the zo
ne of discontinuity is called a cold front.
On the average, cold fronts are about twice as steep as warm fronts, having
slopes of perhaps 1:100.
In addition, cold fronts advance at
speeds up to 80 kilometers
(50 miles) per hour, about 50
percent faster than warm fronts
As the temperature contrast across a front lessens, the front will
often weaken and dissipate. Such a condition is known as frontolysis.
An increase in the temperature contrast across a front can cause it to streng
then and regenerate into a more vigorous frontal system, a
condition called frontogenesis.
Identification and Frontal Weather
Before Passage During
Temperature Warm Sharp drop Colder
Winds South or southwest Variable and gusty West or northwest
Precipitation None or showers Thunderstorms
in summer, rain or snow
Clouds None, cumulus, or
Cumulonimbus None or cumulus in
Pressure Falling then rising Rising Rising
Humidity High, particularly in
Dropping Low, particularly
If a cold front catches up to and overtakes a warm front, the frontal boundary create
d between the two air masses is called an occluded front, or simply an occlusion.
Formation of a Warm Front
Occluded Front Helps to Generate a Mid-Latitude Cyclone
Airflow on both sides of a front is neit
her toward the cold air mass nor to
ward the warm air mass
It is almost parallel to the line of the fro
The surface position of the front does not
move, or it moves sluggishly. This conditi
on is called a stationary front.
Weather Typically Associated with a stationary Front
Some overrunning usually occurs along stationary fronts, gentle to moder
ate precipitation is likely.
Stationary fronts may remain over an area for several days, in which case
flooding is possible.
When stationary fronts begin to move, they become cold or warm
fronts, depending on which air mass advances.