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Storms batter US as winds and heavy rain forecast for UK New Year

Published 24/12/2015

Construction workers John Croft, from left, Michael Edwards and Lee Croft, repair damage to the roof of a chicken house along Arkansas 247 north of Atkins, Ark., near where a woman was killed and a toddler was injured as storms moved through the area Friday morning. (Stephen B. Thornton/Arkansas Democrat-Gazette via AP)
Construction workers John Croft, from left, Michael Edwards and Lee Croft, repair damage to the roof of a chicken house along Arkansas 247 north of Atkins, Ark., near where a woman was killed and a toddler was injured as storms moved through the area Friday morning. (Stephen B. Thornton/Arkansas Democrat-Gazette via AP)

Storms have slammed parts of the southern and Midwest states of the USA in the run-up to Christmas

The storms brought around 20 tornadoes to Mississippi, Indiana and Tennessee on Wednesday alongside thunderstorms, torrential rain and local baseball-sized hail.

Tornadoes are violently rotating columns of air, often associated with thunderstorms, which bring localised swathes of very strong winds. One particularly violent tornado left a 100-mile path of destruction on Wednesday as it ripped through the state of Tennessee, close to Memphis.

The weather will remain unsettled and very wet over parts of the southern states of the USA through the coming days with local flooding and severe thunderstorms affecting areas from Texas north-eastwards to Kentucky and Illinois. Parts of Texas, including the Amarillo area, could also experience some unusually heavy snow just after Christmas.

Meanwhile, eastern states of the USA have been experiencing some exceptionally warm weather in the run-up to Christmas. Indeed, with highs of around 23C in New York on Christmas Eve (the late December norm is only around 5C), residents have been enjoying unseasonable T-shirt-and-shorts weather.

The main cause for these extremes in weather is a large area of low pressure currently located over central areas of the USA. This low pressure area has promoted warm southerly winds from the tropics over eastern states while drawing in cold air to the west. Meanwhile, storms have occurred on the boundary of these two "air masses" where warm, moist air from the Gulf of Mexico has condensed out as torrential rain.

Can this varied weather also be apportioned to the El Nino phenomenon?

El Nino is an ocean-atmosphere phenomenon characterised by persistently above-normal sea surface temperatures in the central and eastern Pacific Ocean.

El Nino has long been recognised, being first observed by fishermen off the coast of South America in the 1600s, who noticed the development of unusually warm water in the Pacific Ocean. Indeed, this phenomenon is a natural one but occurs irregularly, anything from around every two to seven years.

El Nino impacts the weather because it provides an additional heat source, effectively adding fuel to the weather. El Nino can also distort weather patterns across the globe and tends to be associated with a more southerly storm track over the USA, which has been observed in recent days with the severe storms over the southern states.

This year's El Nino has been a particularly strong one and has probably been partly responsible for the recent mild conditions over much of Europe and the UK too.

El Nino blamed for South America floods and drought  

So will the mild conditions continue through the Christmas and new year period in the UK?

After a bright but chilly morning over much of the northern half of the UK on Christmas Day, the coming days will have temperatures mostly near to above the seasonal average with some wet and windy conditions at times.

There is a risk that one or two deep areas of low pressure approach from the Atlantic next week, bringing the threat of stormy winds and heavy rain for western and northern areas in the run-up to new year.

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