Archives for October 2012

First cold snap of the season

Paul Hudson | 15:23 UK time, Thursday, 25 October 2012

After a relentlessly gloomy week, much clearer but colder air is on its way from the Arctic in the next 12 hours, giving us our first cold snap of the season, albeit a short lived one.

Some of us, mainly in eastern parts of the region will see showers, and the air will be cold enough for some of these to have a wintry flavour - with hail, sleet and some snow.

By Friday night, the North York moors and Wolds could have a slight covering of snow, as you can see on the figure below, although this will melt very quickly on Saturday.

Further west, skies will be mainly sunny on Friday and Saturday, with excellent visibility for those who enjoy a bracing walk in the Pennines, but a widespread frost expected at night.

It's perfectly normal to get a cold snap at this time of the year, and it will prove to be temporary, as less cold Atlantic air moves back in on Sunday, bringing cloud and some rain.

But it comes after what has been quite an exceptional few weeks of below average temperatures.

According to climatologist Philip Eden, the period from mid-September to mid-October was the coldest such period since 1974, and in the last century only 1952 and 1905 was colder.

As for next week, it's a familiar story, with low pressure set to dominate, leading to changeable and unsettled weather across many parts of Yorkshire and Lincolnshire, with temperatures at best close to average.

But with winds from the west, there will be some dry, bright weather at times, with eastern areas most favoured.

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Quiet spell of autumn weather on the way

Paul Hudson | 15:23 UK time, Thursday, 18 October 2012

After what has seemed like a relentless period of unsettled weather stretching back to the end of March, it's nice to be able to report that a quieter spell of weather seems likely next week - although talk of an 'Indian Summer', for our region at least, is a little far-fetched.

Friday and Saturday look generally dry, although there will be some fog to contend with in the mornings.

The change will come courtesy of a warm front which will bring some rain and drizzle from the southeast later on Sunday.

Thereafter, the good news is that a ridge of high pressure will dominate our weather, meaning much drier weather on the whole next week.

And at first glance, it is easy to get carried away with the fact that the air which is on its way from the continent is warm.

But, unfortunately for us, it has to travel across the North Sea.

And as it does so, the warmer air coming into contact with the colder North Sea is likely to generate extensive low cloud at times.

In these situations it is possible to get quite high temperatures - for example where there is shelter from the prevailing south-easterly wind, like west of the Pennines, or areas where the warm air only has to travel across a short sea track, like southern parts of the UK.

But for our part of the world, skies are likely to be predominantly cloudy - although with light winds and generally dry conditions (apart from drizzle which can form in extensive low cloud), it should be an improvement compared with what we've been used to.

And let's hang on to the possibility that even here cloud breaks can occur in this set up, leading to at least the chance of some warm sunshine at times.

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A step forward in forecasting cold winters?

Paul Hudson | 15:16 UK time, Thursday, 11 October 2012

Sudden stratospheric warming (SSW) has been the 'in' topic in meteorological circles in the last couple of years, ever since the severe winter of 2009/2010 in which December was the coldest since the late 19th century.

SSW is linked to sudden large increases in temperature over a few days in the stratosphere over the Arctic.

This temperature change cause winds to reverse their normal direction.

For some time, forecasters have noted that a sudden weakening in high altitude winds in the stratosphere was often followed in winter by blocking surface weather systems.

These blocking weather systems tend to bring much colder conditions across Europe and the UK from the east, stopping milder air pushing in from the Atlantic.

There have been notable successes from observing this phenomenon on shorter time scales.

A week before the onset of severe cold that begun at the end of November 2010, stratospheric warming was observed, which led to a forecast which successfully included a risk of cold conditions developing across the UK.

The cold weather which occurred in 2006 and 2010 also coincided with sudden stratospheric warming.

But it would be much more helpful if the onset of such severe weather could be forecast further ahead, and that is what researchers at the Met Office have been working on, publishing research in Environmental Research Letters last month.

A breakthrough came last year when scientists at the Met Office demonstrated a clear link between stratospheric influence on climate during a sudden stratospheric warming, with easterly winds burrowing down through the atmosphere to affect the jet stream.

Following on from this, researchers at the Met Office have produced a model that is better at simulating stratospheric warming, which may give forecasters a better chance of signalling cold winters in future.

By using this new model with data available from autumn 2009, the Met Office showed that they could have seen the cold coming well in advance.

But blasts of cold weather are not always due to SSW.

There are several competing influences each winter, such as Atlantic sea surface temperatures, volcanic eruptions, snow cover and solar forcing.

For example, the research highlights the deep solar minimum as a contributory factor to the observed severe weather conditions in 2009/2010.

But separating their effects, and establishing which has the largest impact, remains a big headache for forecasters.

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Regional and global climate update

Paul Hudson | 17:10 UK time, Thursday, 4 October 2012

Provisional Met Office statistics show that September across the UK was wetter than normal with 112mm, or 117% of the long term average.

It was also cooler but sunnier than normal.

Regionally, the North of England was much wetter than the rest of the country, with 133mm of rain, which is 165% of average, making it the wettest since September 2000.

It was also the 6th successive month where rainfall was above normal.

There were contrasts across our region though.

Yorkshire received 125mm or 170% of average rainfall, but Lincolnshire was much drier, with only 43.4mm or 80% of the long term average.

The unsettled theme looks set to continue, with more rain tonight and early next week, which could be potentially heavy, although the weekend is looking fine and dry.

Normally at the start of the month I update the UAH satellite global temperature for the previous month, for no other reason than it's published before any of the other measures.

But for technical reasons, which you can read about here, this is not yet available.

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