Summer forecasting and the importance of local effects

Following on from our Chief Meteorologist explaining a little about why it is more challenging to predict the weather in summer, I have asked Ewen McCallum to explain the science of summer forecasting and the importance of local effects:

Do you ever wonder why the weather can change so much from place to place, especially in summer. Well its all down to a complex word called ‘topography’. That’s just a fancy word for the shape of the land and sea that you see when you fly across the country in an aircraft. In fact a lot of the weather we experience is because of the shapes of the hills, valleys, coasts and rivers and how the air flows around them.

In summer the large scale lows and weather fronts of winter are often absent and so local variations in temperature and moisture often dictate what the weather will be. To complicate matters in the UK the atmosphere is often in a finely balanced situation such that if the air ascends it will keep going up until it cools and forms shower clouds. So showers often form over hills as the air is forced to rise over them. Also at the coasts we often witness a cooling breeze as the land heats up and rises drawing in cooler air to replace it from the sea. Now as this air rises inland if conditions are right showers can form. Often they form into lines and so some people can get a soaking from one shower after another whilst other people at the coast wonder what all the fuss is about.

It is not just showers that are affected by ‘topography’. Low cloud often sits on the upwind side of a hill or on top of the hill but if you drive to the lee of the high ground it could be bright and sunny. If you are sitting on the beach with fog rolling in off the sea go inland where the sun will heat the land and burn the fog away.

So understanding your local topography and which way the wind is blowing will help you add value to the national weather forecast and could make your holiday more successful.

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