1. Standard Grade Weather Depressions

2. Today we are going to learn..  What a depression is  The main features of a depression  The weather associated with a depression

3. What is it?  Depressions are areas of low pressure which bring rain, cloud, wind and unsettled conditions  They form when warm, tropical air from the south meets cold, polar air from the north  The boundary between the two air masses is called a front  They are shown on synoptic charts

4. A Depression isobars

5. Isobars close together = strong winds Winds flow in anticlockwise direction Low pressure = < 1000 mb High pressure = > 1000 mb

6. Main features  When the two air masses meet the lighter, warm air is forced to rise above the denser, cold air forming fronts  As the warm air rises it cools, water vapour condenses, forms cloud and then frontal rain  Where the cold front travels faster than the warm front and catches up, an occluded front is formed  Depressions travel from west to east across the UK

7. Depressions move from West to East Warm sector

8. What have we learnt so far? Always moves west to east COLD AIR WARM AIR Winds blow anticlockwise WARM SECTOR COLD FRONT WARM FRONT OCCLUDED FRONT This is a Low Pressure System, commonly known as a Depression TASK: Add labels to your diagram of a depression Cold sector Isobars are close together Air pressure is below 1000mb

9. Tasks Depressions are very ______ areas of ____ pressure. They bring _________ weather. On ________ weather maps they are represented by upside down ____. They form when _______ air rises over ______ air. A typical depression passes over the UK from _____ to _______. COLDLOWWESTLARGEV’S UNSETTLEDEASTWARMSYNOPTIC

10. What is the weather like? OCCLUDED FRONT Cold sector Weather fair but beginning to cloud over as warm front approaches. Temperatures cool WARM FRONT Brings cloud, steady rainfall and strong wind. Temperatures rise WARM SECTOR Slight drizzle as skies clear and rain stops. Temperatures still warm COLD FRONT Heavy rainfall, thick cloud cover, strong winds and lower temperature. Cold sector Skies clear as rain stops. Wind lessens. Temperature remains cool

11. What is the weather like?  As the warm front approaches it brings steady rainfall, low cloud and strong winds  In the warm sector the temperature rises, the cloud breaks and winds drop, often a small period of dry weather  As the cold front approaches, winds can become gale force, temps drop and rain becomes very heavy  As the depression passes, rain eases and winds, although cold, begin to drop

12. Warm sector Prolonged, steady rain Heavy rain Heavy showers with sunny intervals Drizzle/fair Sunny/fair EAST WEST

13. Occluded Fronts  What is it?  Occluded fronts happen when the cold front travels faster than the warm front and overtakes it.  Weather?  Strong winds, storms, thick cloud and rain TASK: Write a definition for occluded front, don’t forget to draw the symbol.

14. Tasks 2. Use page 80 of new key geography GCSE to draw the diagram of a cross- section of a depression. Add labels and colour it in. 4. Collect a copy of ‘What happens When a Depression Passes over Musselburgh?’ Use the following slides to help you write a description of the weather in Musselburgh at each stage. Glue it into your jotter.

15. What happens when a depression passes over Musselburgh? Temperatures are cool because Musselburgh is in the cold sector of the depression. Clouds are beginning to form. Winds blow from the South west. Temperatures rise as warm front arrives. It is now raining heavily as the warm front is over Musselburgh. Winds are blowing from the west.

16. Temperatures are cool because Musselburgh is in the cold sector of the depression. Skies are clearing. Winds blowing from the north. Temperatures are cooling down as the cold front arrives. It is now raining heavily because cold front over Musselburgh. Winds blowing from north west. Temperatures are warm as Musselburgh is in the warm sector of the depression. Weather is dry, winds are blowing from the west

17. Tasks:  Collect a copy of the air pressure past paper questions from the front. Answer the questions in your jotter.  Look through your notes to help you answer the questions.