1 Low pressure areas or depressions

2 Last week we saw why sometimes we get clear skies and warm sunny weather But we haven’t had much at that this year!

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4 Why? We have had a lot of low pressure areas called Depressions

5 At this point … I hope we can watch a BBC video which explains it a rather well lips/s_geog/bb/s_geog_ec_02985_4x3_b b.asx

6 Warm air and cool air do not mix Between 45N and 64N cold air from the poles meets warm air from the topics to form a polar front

7 As warm air meets cold air, the temperature gradient is strengthened This leads to instability and a wave forms that develops into a triangular shape – warm air inside the triangle and cold air outside it

8 The leading edge of the depression is called the warm front. Here the warm air, which is lighter rises above the cold air in front of it. The cold air moving behind the warm air travels faster and pushes its way under the warm air. This is a cold front

9 At the top of the triangle pressure falls as the warm air rises in a spiral movement. Winds develop and blow around the centre of the low pressure in an anticlockwise direction. The boundary between the warm air and the cold air is called a front

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12 Cool to cold or warm? Any cloud? Any precipitation? Wind?

13 Cool to cold or warm? Any cloud? Any precipitation? Wind?

14 Cool to cold or warm? Any cloud? Any precipitation? Wind?

15 Cool to cold or warm? Any cloud? Any precipitation? Wind?

Behind the cold front At the cold front In the warm sector At the warm front Ahead of the warm front It remains cold Clouds thin The wind is still a bit blustery There are showers. There’s a sudden drop in temperature Clouds thicken into big cumulonimbus clouds Wind speeds increase, sometimes to gale force There’s heavy rain, sometimes with hail, sleet and thunder. The temperatures are mild The cloud becomes thinner and breaks The wind steadies The rain turns to drizzle and stops Temperatures continue to rise The clouds get thicker and lower (known as nimbostratus) The rain is continuous and sometimes heavy the wind veers and becomes blustery There is high thin cloud called cirrus No rain at first It is quite cold but the temperatures start to rise wind speeds increase What are the expected weather conditions at each stage of a depression as it crosses Britain? Reading to learn!

17 Marge decides to give up on a day outdoors as the rain hasn't stopped for hours! She decides to go shopping instead. Strong winds nearly blow Bart off his skateboard! Lisa checks out her ‘Guide to Clouds’ book to find out the name of clouds that are high in the sky! “Grampa” switches on the news to hear that a weather depression going to affect Britain soon Maggie cheers up when the sun comes out! Bart finds a new jacket in the park that’s just his size! “Excellent”, he says, “its started to get cold and it looks like it might rain!” Chief Wiggum ventures out of his police car after heavy rain and thunder to buy his coffee and doughnut. He wasn’t expecting to get caught in a rain shower! Where in the depression...? Read the following statements from characters in ‘The Simpsons’. Decide which section of the depression (1-5) they are most likely to be referring to. Write your chosen number it in the box next to each statement. Be ready to justify your decisions! Categorising information and making decisions to learn! Challenge! There are two blank speech bubbles. Create two appropriate statements for a stage of the depression

18 n_and_fronts/eng/Int roduction/plenary.htm n_and_fronts/eng/Int roduction/plenary.htm Go to the 3 rd part