What’s up with the weather?

Cuillin is more interested in smells than a rainbow over Loch na Cleitichean. Photo by Eddie Graham.
Cuillin is more interested in smells than a rainbow over Loch na Cleitichean. Photo by Eddie Graham.
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The Met Office has confirmed that the UK has just experienced the wettest ever December-January period on record.

Across the Hebrides, more than twice the average monthly rainfall fell during December and it was one of the stormiest months experienced for decades. And when the storm track moved south in January, it was the turn of south-western coasts of England, Wales and Ireland to experience enormous waves and tides, as well as torrential rain and flooding on an unprecedented scale. So what on Earth is up with our weather at the moment? Is global warming and climate change to blame?

In attempting to answer these questions, one must first look at the direct meteorological cause - which has been an unusually deep area of low pressure anchored off western Ireland since early December. Whilst spells of bad weather can be expected across Scotland every winter, what has been unusual about this season’s low pressure is that it has been (i) located much further south than normal (the lowest pressure is usually found much further north near Iceland), and (ii) each of the individual storms spawning from this weather system has been extraordinarily intense, in many instances deeper than those of major Caribbean hurricanes!

This change in position and intensity of the low pressure system has meant that much bigger waves than normal have been generated in the Atlantic seas off Britain and Ireland. The very low air pressure has also meant that there is less weight of air on the sea surface, as air pressure is simply a measure of how heavy air is. This has actually caused the sea surface to ‘rebound’ or rise-up higher than normal, contributing to some of the enormous tides seen across the British Isles recently.

And what has caused the low pressure to behave in this unusual way?

Here, one may simply answer: “What doth blow the wind?” What I mean by this, in essence, is that all weather systems around the world are linked together in some way or another.

When a change in weather happens in one place, it feeds back into the developing weather systems somewhere else, and so on. Hence, we might equally blame our poor winter weather on the very cold conditions in North America, or on a stronger than normal ‘Jetstream’, or on warmer than normal sea-surface temperatures in the Tropics. All of these weather events elsewhere in the world may have helped to cause, directly or indirectly, this winter’s floods and storms. The atmosphere is extremely complex and dynamic system and it can never be predicted with absolute certainty.

Could global warming be partly to blame?

As far the UK Met Office is concerned, the ‘jury is out’ on the possible contribution of climate change to the recent storminess and flooding. The climate of the British Isles is highly variable, and thus extremes in weather can be expected to occur from time-to-time. Nevertheless, some studies have suggested there has been an increase in the intensity of Atlantic storms and hurricanes. There is also an increasing body of evidence that shows that extreme rainfall events are becoming more intense, which is consistent with what might be expected from the physics of a globally warming world.

January 2014 Weather Summary

The main feature of January’s weather was the milder than average conditions, with no lying snow reported and there were only two nights when a slight frost was recorded. Overall, total rainfall, sunshine and wind speeds were close to normal. But such was the wetness of the preceding December that we had already received our full quota of winter (December +January+February) rainfall by the end of January .

Averaged daily high+7.4°C (Highest: +9.2°C on 6th)

Average daily low: +3.1°C (Lowest: -0.9°C on 12th)

Deviation of average temperature from normal: +0.7°C

Total precipitation: 168.6mm (6.63in) ; very close to normal

Wettest day: 36.0mm (1.41in) on 26th

Average wind speed: 17.0mph (14.8 knots); close to normal

Highest Gust: 65mph (56 knots) on 26th

Sunshine: 28.5 hours (about 90% of normal)

Number of air frosts: 2 (significantly below the average of 6) No days with lying snow were recorded.

All readings taken in Stornoway.