What is an Occluded Front?
The Formation of an Occluded Front
http://covis1.atmos.uiuc.edu/guide/fronts/occluded.html
The diagrams above show the formation of an occluded front. When a depression (or a low pressure system) forms, it usually consists of a warm front and a faster moving cold front. This can be seen in the top left diagram. To the north of the warm front is the cool air that was in the area before the depression developed.
As the depression intensifies, the cold front catches the warm front. This can be seen in the top right diagram and in the diagram below. The line where the two fronts meet is called an occluded front. When an occluded front passed overhead, you would feel changes in temperature and wind speed.
An Occluded Front
http://206.251.19.76/weather/wofront.htm
There are two different forms of occluded front. One is called a cold occlusion. This can be seen in the diagram below.
http://206.251.19.76/weather/wofront.htm
A cold occlusion occurs when the air behind the occluded front is colder than the air ahead of it. The cold occlusion acts in a similar way to a cold front in that the the cold air behind the front undercuts the cool air ahead of it.
The other type of occluded front is the warm occlusion. This can be seen in the diagram below.
http://206.251.19.76/weather/wofront.htm
A warm occlusion occurs when the air behind the occluded front is warmer than the air ahead of it. The warm occlusion acts in a similar way to a warm front in that the cool air behind the front is lighter than the cold air ahead of the front. This causes the cool air to pass over the top of the cold air.
We are now going to look at a weather map from the Electronic Telegraph web site. This will help us understand how to recognise an occluded front.
Occluded Front Over the UK on the 25th March 1998
http://www.telegraph.co.uk |
This chart shows the progression of an occluded
front over the UK on the 25th March 1998. The front is represented by the black
lines. It travels in the direction that the wind is - in this case in an
anticlockwise direction. You can see that the weather conditions ahead of, within
and behind the front are different.
What is the change in temperature ahead of, within and behind the warm front?
What other weather conditions change ahead of, within and behind the front? |
The following photograph shows the weather conditions at the Moor House site located in the northern Pennines. Click here to see the Moor House site map.
What does the photograph show to make you think that there is an occluded front over the site at the time?
Do you think that you could now spot an occluded front on a weather map? Have a look at today's weather for the UK (on BBC weather site). Write down whether you think the UK has a warm, cold, or occluded front over it. To return to this page click the back arrow at the top left of your screen.
You have now finished the tutorial on occluded fronts. Would you like to choose a new tutorial, or return to the fronts tutorial?
