BBC News

Why does it always rain on May?

By Steven McKenzie
BBC Scotland Highlands and Islands reporter

image copyrightThinkstock

May has been a wash out.

Traditionally, the month is held up as one of Scotland's best for fine weather - and with biting midges still to emerge.

But few places have escaped heavy downpours and chilly temperatures this May.

BBC Scotland weather presenter Christopher Blanchett explains why, while meteorologist Dr Edward Graham, of the University of the Highlands and Islands, looks into a suggestion made earlier this week that the weather is getting more extreme.

image captionSome of May's weather has blown down from Greenland

"We should be experiencing temperatures into the mid teens by the end of May, but instead it has been a good deal cooler," says Blanchett.

"It's all down to where the weather and where the land mass it sits in has been coming from.

"North westerly winds have fed in the cool conditions from places like Greenland along with spells of wind and rain.

"The reason is partly down to the position of the jetstream, high level winds in the atmosphere.

"The jetstream has been to the south of us meaning we are in the cooler air on its northern side. It has also meant more frequent low pressure systems bringing wind and rain."

But the weather presenter added: "There are signs of change. As the jetstream moves north it will bring more settled, and crucially, warmer weather."

image copyrightThinkstock
image captionThe west of Scotland has got wetter since the 1970s, says Dr Graham

Extreme weather has been increasingly disrupting ferry sailings on Scotland's west coast, according to ferry operator Caledonian MacBrayne.

CalMac said the masters of its ships have experienced bad weather of greater severity and lasting for longer than previously seen.

Lewis-based Dr Graham says it is correct to say the weather on the west coast has got worse over the past two winters.

"But that was on the back of two of the quietest winters on record, 2009-2010 and 2010-11," he adds.

The meteorologist says the weather should sooner or later get better again.

He says: "It's nearly all down to the North Atlantic Oscillation (NAO), a dominant weather pattern over the North Atlantic Ocean.

"The higher the NAO value is during the winter, the stormier the weather is, and the bigger the waves.

"But the fly-in-the-ointment is of course, climate change - are such winters becoming more regular, rather than isolated cases?

"Again, yes, there is some evidence of an increase in extreme types of weather around the world due to climate change, but no specific studies that I am aware of are conclusive on the state of the climate of the west coast of Scotland.

"For example the west of Scotland is certainly getting warmer - about 0.5C warmer - and is getting wetter since the 1970s.

"But there's conflicting evidence on winds.

"Stornoway Airport actually shows a reduction in average wind speed during winter of about minus one knot, but this is probably non-significant and may be due to simple changes of instrumentation.

"Some evidence indicates individual storms are getting more severe, but there are actually slightly fewer of them."

Related Topics

  • CalMac
  • University of the Highlands and Islands
  • Isle of Lewis

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