La Niña to make winter months Colder across the UK
Forecasters have predicted an increased chance of a colder-than-usual start to this winter due to a change in Arctic conditions and ‘unusual’ tropical rainfall patterns.
The Met Office said the conditions mean there is a 30 per cent likelihood the mercury will plunge at the beginning of this winter – the highest risk of a cold start since the bitterly cold season of 2010/11.
But the agency said it was too early to predict whether it would be a snowy, wet or dry three-month period from November.
[image: hand-written message in frost on a windscreen of a car in Culgaith, Cumbria, this morning]
The key factors leading to colder temperatures include ‘disturbed’ stratospheric Arctic winds known as the polar vortex, which affects the jet stream, and a La Niña, the opposite of an El Niño, bringing lower temperatures in the tropics.
The Polar Vortex hit the US hardest in 2014, affecting 200 million people and causing billions of dollars in damages, but climatologists think it won’t be as severe this time around.
But the Met Office pointed out there was still a 70 per cent chance of milder temperatures and, following a reversal in expected atmospheric patterns in February this year, the prevailing westward winds could increase the chances of warm and wet conditions. Forecasters reached the long-range prediction after feeding their analysis of those factors into a computer model, with the result higher than the expected 20 per cent probability suggested by a 30-year rolling average up to 2010.
Professor Adam Scaife, head of long-range prediction at the Met Office Hadley Centre, said: ‘The risk of a cold start to winter has increased to 30 per cent this year.
‘Statistically, however, it is still more likely that the UK will experience a normal start to winter, but there is an increased risk of cold snaps between now and Christmas.’
He added this does not necessarily mean we will get large amounts of snow.
‘Several factors, including tropical rainfall, are known to drive UK and European winter conditions: following a strong El Niño last year, the tropics are now influenced by a weak La Niña and unusual rainfall conditions in the Indian Ocean.
‘Historical weather observations and our latest computer model simulations agree that these factors are increasing the risk of a cold start to winter for the UK, but this is unlikely to persist through winter as a whole.’
As many parts of Britain woke to the first taste of winter, with white-frosted lawns and car windscreens needing de-icing this morning, the cold weather looks set to continue. Meanwhile, a study published in October suggested warming in the Arctic is influencing the jet stream, a high-altitude corridor of fast-moving air.
It is thought this could have caused severe cold snaps such as the record snowfall in New York during the winter of 2014/15, and unusually cold winters in the UK in 2009/10 and 2010/11.
The winter of 2010 saw the UK’s coldest December in records stretching back 100 years.
Studies have shown that when the jet stream follows a ‘wavy’ irregular path there are more cold weather fronts plunging south from the Arctic into mid-latitudes, bringing freezing conditions that persist for weeks at a time.
The Climate Prediction Centre (CPC), an agency of the National Weather Service in the US, in a monthly forecast pegged the chance of La Niña developing this autumn at 70 per cent.
The Met Office said the conditions mean there is a 30 per cent likelihood the mercury will plunge at the beginning of this winter. The conditions are slightly favored to persist into the winter, CPC said, pegging the chances at 55 per cent.
The emergence of La Niña would follow a strong El Niño that has dissipated in recent months after wreaking havoc on global crops.This new forecast goes in contrast to the neutral conditions predicted last month, which claimed that the onset of such an event would be unlikely.
An animation from the CPC shows how temperatures in the equatorial Pacific have recently begun to cool to levels that are uncharacteristically low. The Polar Vortex is on the move unusually early this year, forecasters revealed last week – and say it could strike the US in January.
A recent study claimed Arctic sea-ice loss is causing the Polar Vortex to shift and as a result, winters are expected to get longer and more bitter. Last week forecasters said it is ‘unprecedentedly early’.
The Polar Vortex hit the US hardest in 2014 , affecting 200 million people and causing billions of dollars in damages, but climatologists told MailOnline last week that, thankfully, it won’t be as severe this time around.
‘The winter of 2014 was a really extreme case, as the cold was so persistent and it was focused on one area, which makes it very hard to reproduce,’ Judah Cohen, a climatologist at Atmospheric and Environmental Research (AER), a Verisk Analytics Business said.
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