Download what is a depression

What is a depression (UK)?
This aerial view shows the fronts, sectors and other features of a
depression. Click here to find out about the fronts. The pink area is called
the warm sector (this is the warm area of air which the warm front is at
the front of. This system rotates anticlockwise and winds blow in towards
the centre.
Depressions are low pressure systems which bring wet weather to the UK.
As the air is rising in the centre of the system, it cools and condenses to
form clouds. Winds move anti-clockwise towards the centre, where they
are heated up and they rise. The cross-section diagram above shows the
position of the fronts and the effect that this has on the air. In short, the
COLD FRONT and the WARM FRONT rotate in an anti-clockwise direction
and the cold front moves faster than the warm front. Between the two
fronts is the area of warm air called the WARM SECTOR. Eventually, when
the cold front catches up with the warm front it lifts the warm sector off
the ground and creates an OCCLUDED FRONT. If you want to know more
about
fronts,
click
here!
If the * symbol were to indicate a person standing in the path of a
depression for 12 hours, this is the weather that person would experience
as
the
depression
moved
EAST
over
that
position:
12 pm - cold temperatures, hazy cloud (getting cloudier) and drizzly rain.
This is because the person is stood under the warm front, which is much
gentler than the cold front. Air rising up this, cools much more slowly. As
the front is gentler, it is spread out over a larger area, and so is the rain.
6 pm - warm temperatures, hazy or clear skies, no precipitation. At this
point the person would be stood in the warm sector of the depression,
hence
the
warmer
temperatures
and
clear
sky.
12 am - cold temperatures, sky obscured by clouds, very heavy rain,
clearing to the west. After the warm sector a steeply rising , fast-moving
cold front approaches. As it pushes into the warm air of the warm sector,
air is forced to rise stepply and rapidly, cooling quickly as it does so. The
front is steep, so rain is spread over a smaller area, making it heavier. As
the cold front passes over, the temperature drops considerably as the
person is stood in the colder air mass. Clearing from the west, the sky
becomes less obscured and cumulus clouds can be seen.