5 Jan 2016

December 2015 was UK’s wettest month on record

It’ll come as no surprise that the Met Office announced today that December 2015 wasn’t just the wettest December on record, but also the wettest calendar month on record for the UK.

Copious amounts of rain fell during December 2015, as three named storms – Desmond, Eva and Frank – affected the UK and Ireland.

The storms not only brought heavy rain and flooding, but severe gales, which caused disruption to travel and power supplies.

YORK, UNITED KINGDOM - DECEMBER 28: Rescue teams wade through flood waters that have inundated homes in the Huntington Road area of York after the River Foss burst its banks, on December 28, 2015 in York, United Kingdom. United Kingdom. Severe flooding has affected large parts of northern England, with homes and businesses in Yorkshire and Lancashire evacuated as rivers burst their banks. More heavy rain is forecast as dozens of severe flood warnings remain in place. (Photo by Jeff J Mitchell/Getty Images)

Thousands of homes were flooded in Scotland, northern England and Ireland as flood defences failed to cope with the abundance of rain flowing through the river systems.

How much rain actually fell?

The wettest parts of the UK were north Wales, northern England and parts of Scotland, where more than three times the average December rainfall fell.

In terms of individual nations, Wales and Scotland had their wettest December on record, with 217 per cent and 215 per cent of their average monthly rainfall respectively.

Between the 1-28 December, Capel Curig in Conwy shattered its December rainfall record, with more than a metre of rain (1012mm). The previous record stood at 613mm.

Shap in Cumbria also set a new December rainfall record by a significant margin, with 773mm compared with the previous record of 504mm.

wet_december_MO_wpWhy so wet?

The month of December was characterised by a persistently strong jet stream over the Atlantic Ocean, which spawned a number of storms and then catapulted them towards the UK and Ireland.

Stormy weather at this time of year isn’t unusual, but its persistence and the amount of moisture within these rain bearing weather systems was significant.

Whilst climate change is an obvious contender for influencing severe weather, it is very difficult to pinpoint individual spells of weather as solely down to climate change.

However, a warmer atmosphere can hold more moisture and thus produce more rainfall. So, it would be true to say that the trend of more intense rainfall would fit in with the expected trends in a warming world.

El Nino’s influence

A much more likely influencer of our phenomenally wet spell is El Nino – the marked warming of the ocean waters in the eastern Pacific Ocean.

Even though El Nino seldom has a direct effect on the weather in Europe, the way in which it affects atmospheric patterns elsewhere in the world can have an indirect impact on our weather.

In a recent blog from the Met Office’s chief scientist, Professor Dame Julia Slingo, she explains that unusual warmth in the north east Pacific Ocean may have altered the position of atmospheric waves, which determine where stormy weather patterns will hit.

This, combined with warmer than normal ocean temperatures in the southern Atlantic Ocean, meant that our storms had more moisture within them than would typically be expected – therefore producing more rain.

When will it stop raining?

The rest of this week will see low pressure remain close to the UK, bringing further showers or longer spells of rain at times.

However, the rain won’t tend to be as intense or as prolonged as what we saw during the Christmas period – meaning that the flood risk won’t be as high.

Better news comes towards the middle of January, when the jet stream is going to weaken and move well south of the UK.

high_midjan_WZ_wpThis will allow high pressure to form over or close to the UK and Ireland, bringing drier and colder weather – something that will be a shock to the system after last month being the warmest December on record.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website. I’ll also be posting updates on Twitter – @liamdutton

Final image: Wetterzentrale

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