Monday 20 November 2017

Unseasonal conditions brought feeling of near euphoria

Prof John Sweeney

THE dark days of December usually bring a host of moans and groans about the weather in everyday casual conversation.

And while we have been battered by some violent storms of late, we have also enjoyed a run of unseasonal conditions across most of the country over the past six months. After the seemingly never-ending winter and delayed spring of 2013, a truly exceptional summer and autumn occurred bringing a spell of weather euphoria.

Who can forget the best summer in years when Met Eireann declared heatwave conditions in July with a run of five days above 25C, culminating in tropical temperatures over 30C on July 19?

Who can forget the official declaration of drought in Ireland that same month when more than 15 days produced no significant rainfall?

Perhaps there was a feeling that we would have to pay for this in the autumn and winter.

Certainly, the usual unscientific prophets of gloom were trotted out to feed this fear.

But instead, the Irish weather system has, by and large, behaved itself admirably. Autumn (September-November) has turned out to be warmer and drier than usual, by up to 7C.

Even in the third week in September the thermometer touched close to 24C and nature provided a particularly colourful landscape as the Indian summer lingered.

While November was cooler, it was the relative dearth of rain which was most remarkable. It has been the driest autumn in most parts of Ireland for six years, and in some western parts for up to 20 years.

In Dublin's Phoenix Park it was the driest November since 1945. There is also a feeling that Ireland 'dodged a bullet' with most of the autumn storms.

Violent winds caused severe damage in Cork last week and a life was tragically lost when a tree fell onto the road in Westmeath. But fortunately the 'St Jude' storm at the end of October and the more recent Windstorm Xaver on December 7 -- which brought fatalities and damages estimated at around €1bn in the UK -- provided only a glancing blow on Ireland.

The key to these events is as ever provided by the location and behaviour of the jetstream, fast flowing ribbons of air around 10km above the surface.

These steer (and help form) the disturbances which bring wind and rain to Ireland.

For much of summer and autumn the jetstream pushed depressions away from us, either to the south or around the north of Scotland into the North Sea. For a time they followed twisting, convoluted paths which allowed anticyclones to feed up tropical air from as far away as West Africa.

As recently as two weeks ago we enjoyed such a burst of tropical air, bringing temperatures of around 15C to our short December days.

Since then it has been wet and windy, with strong winds causing problems particularly in the west and north-west over the weekend. But as long as our airmass comes from the west, across a sea which is still at 11C, real extremes of cold are unlikely.

Only brief incursions of polar continental air (helping the sleigh from Lapland) are likely to occur, so a dramatic freeze seems unlikely as we reach the year's end.


Irish Independent

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