Climate change means wetter winters

Tuesday 24 November 2009, 16:49

Derek Brockway Derek Brockway

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Earlier this Autumn we enjoyed some fine and warm weather but its all a distant memory now with flooded fields and swollen rivers a feature of the countryside.

I bet most of you will be glad to see the back of November. In a recent blog I mentioned the poet T. S. Elliot who described November as being a 'sombre month'.

Recently, I received a letter from Martin Blackmore from Sketty in Swansea who sent me a copy of a poem by Ted Hughes called 'November'. In it Ted describes November as "the month of the drowned dog". I tend to agree! ;)

The recent record breaking rainfall in Cumbria was caused by a combination of factors. A constant supply of warm and moist air from the Atlantic and very strong south-westerly winds.

As the air hits the high ground in the Lake District the air is forced to rise upwards creating more condensation, clouds and rain.

In meteorology, this process is called 'Orographic Enhancement' when rainfall in the mountains can be at least 10 times greater than on the coast.

In Wales, November is the third wettest month of the year with an average rainfall of 156.8mm.

So far this month we've exceeded that with 241.8mm of rain but some mountainous areas have had more than this!

At our weather station at Dyffryn Mymbyr near Capel Curig in Conwy, 496.6 mm of rain has fallen so far this month, way in excess of the November average of 285.6 mm for that location.

  • The wettest day in Wales was at Lluest Wen Reservoir in the Rhondda Valley on November 11th 1929, with 211.1mm of rain in 24 hours.

  • While the wettest November in Wales came in 1965 with over 311mm.

  • Late October and early November 2000 also saw severe flooding with over twice the normal rainfall.

The River Dee in North Wales burst its banks and landslides also occurred in early February 2004, around Llanwrst in the Conwy valley of North Wales.

Preceding this, there was prolonged heavy rainfall across Snowdonia, with over 300 mm of rain falling at Capel Curig in just 6 days.

As climate change takes hold, winters in Wales are expected to become milder and wetter with less snow and more storms.

Warmer air can hold more moisture so more intense downpours are likely too with an increased risk of flooding.

In the short term, an active cold front will cross Wales tonight bringing a short spell of heavy rain accompanied by very squally winds.

Wind gusts around 70mph are possible on exposed coasts in the South and West and the odd isolated tornado is possible too!

Wednesday will be brighter and colder with a mixture of sunny intervals and showers. Most of the showers in the south and west.

Some heavy with a risk of hail and again it will be windy. Temperatures lower than today 9 to 11 Celsius with a strong to gale force South Westerly wind.

Derek

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