WHAT IS A FRONT?
Fronts = the boundaries between air massesA front is defined as the transition zone between two air masses! As an example in the diagram below there is a front that exists between the advancing cold air mass and the retreating warm air mass. A cold front is the LEADING edge of the cold air mass. A warm front is the LEADING edge of a warm air mass.
One thing to always remember: Cold air is denser than warm air. Colder air is always on the bottom
pushing around the warmer air up and out of the way.
THERE ARE FOUR MAIN TYPES OF FRONTS:
(Cold, Warm, Occluded, Stationary)COLD FRONTS:
A cold front shows the advancement of cold air into a region of warmer air. Interactions along the edge of this front often results in showers and storms developing, as the warmer air is pushed upward by the advancing colder air. Usually the precipitation will last only a few hours as the front passes
There is typically a noticeable temperature change from one side of a cold front to the other. In the map of surface temperatures to the right, 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.
Common characteristics associated with cold fronts have been listed in the table below.
Weather Change
Temperature From warm humid air to colder less
humid air
Pressure The air pressure steadily increases
Precipitation front is passing which could last aboutShort Period of Showers while the 2 to 3 hours
WARM FRONTS:
Warm Fronts are regions of warm air that are advancing on colder air. Warm fronts usually move more slowly than cold fronts. Warm front usually have continual and prolonged precipitation lasting several hours or more. Warm fronts on a map are red and have scalloped edges pointing towards the cool air it's attempting to override.
Weather Change
Temperature From cool temps to warmer temps
Pressure The air pressure steadily drops
Precipitation
Long Period of Showers while the front is passing which could last up to 24
hours
STATIONARY FRONTS:
Stationary Fronts are pretty much just that: Stationary. The two air masses just don’t move. The weather along these fronts is similar to warm fronts, less turbulent, but often longer lasting.
HOW ARE FRONTS DIAGRAMMED?
In order to understand the weather, you have to understand the “language” of weather maps. Pay close attention and you will be able to understand the weather report on the nightly news and explain it to you parents.
The COLD FRONT:
The leading edge (the moving portion) of a cold front is always indicated by a blue line with forward pointing blue triangles.
Blue line with blue triangles = cold front (ahead of the cold air mass)
The map below shows a typical weather map of a cold front. Notice that the cold air is moving to the east (to the left). Notice that the temperatures behind the cold front are much cooler then the warm air ahead of it. In the next few hours, the warm air ahead of the cold front will be replace by that cold air!
The WARM FRONT:
The leading edge (the moving portion) of a warm front is always indicated by a red line with forward pointing red semi-circles.
So, in the picture to the right, the warm air mass is moving up, and the cold air mass is moving down and to the left – trying to fill in the area behind the warm air mass.
The STATIONARY FRONT:
When a warm or cold front stops moving, it becomes a stationary front. A stationary front is represented by alternating blue and red lines with blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air.
HOW DOES PRECIPITATION FROM?
Precipitation Along a Cold Front
(precipitation when a cold air mass overtakes a warmer air mass)
Animation by: Hall
As the front advances, the colder air lifts the warmer air ahead of it (red arrows). As the warm air rises, it condenses to produce clouds and precipitation.
If condensation of water vapor persists, precipitation may develop, typically in a narrow band just ahead of the cold front.
Due to the steep slope of a cold front, vigorous rising motion is often produced, leading to the development of showers and occasionally severe thunderstorms.
Precipitation Along a Warm Front
(precipitation when a warm air mass overtakes a colder air mass)
Animation by: Hall
Since warm air is less dense then cold air, the leading edge of the warm front has a tendency to move up and over the colder air mass ahead of it. As the warm air rides up and over the cold air mass it produces clouds and rain. The clouds and rain actually occur many hours before warm air actually arrives to the area. Because the lifting of the warm air is very gradual and steady, generally widespread and light intensity precipitation develops ahead of a warm front.
A Closer Examination of the Animation:
Initially, a warm air mass (in yellow) nudges against a colder air mass (in blue) ahead of it, (separated from each other by the warm front). The lighter warm moist air behind the front is lifted upward and "overrides" the colder air.
A layer of thin clouds is occasionally observed more than a 400 miles in advance of a surface warm front. As the front gets closer, the clouds thicken and eventually light precipitation begins to fall.
