Mid-week summary

In the next Step you’ll be able to consolidate what you’ve learnt so far by reading a weather map. Let’s first summarise what has been covered.

• Weather systems act to even out the pole to equator temperature gradient.
• Winds are trying to even out the pressure gradient.
• The wind blows around the depression in an anticlockwise direction in the Northern Hemisphere, following the pressure contours.
• The three dimensional processes are key – they lead to cloud, rain and energy being released.

The damage caused by a depression is governed by:

• The pressure difference, which in turn determines the wind speed.
• The time of the year, if the trees are in leaf, they offer more resistance to the wind and are more likely to be blown over.
• The preceding weather – if the ground is already waterlogged, flooding is much more likely. Also, trees and walls are more likely to collapse if on waterlogged ground. On the other hand, if the ground is bone dry and there is heavy rain, the water will run off rather than soak into the soil, and there is the risk of flash flooding.
• The path of the storm, and whether it passes over land or sea, or highly populated or less developed areas.
• The state of the tide – coastal flooding is much more likely if a storm coincides with a particularly high tide.
• Forecast accuracy – if people have notice to avoid travelling, keep high sided vehicles off roads etc. then the damage and disruption can be reduced.