Ireland

It is high summer. So why is it so cold?

The reason for the chilly start to June is the polar front jet stream is currently to the south of Ireland, according to Met Éireann’s Joanna Donnelly

The jet stream is responsible for sustained hot or chilly weather in Ireland, depending on its position. Photograph: Olena Siemer/Alamy/PA

Tim O'Brien
Mon Jun 17 2024 - 13:13

It is high summer. So why is it so cold?

With just days to go to the solstice, a polar airflow is making high summer decidedly chilly.

It is a far cry from June 2023 when Met Éireann recorded the hottest June on record with a temperature of 28.8 degrees at Oak Park, in Co Carlow, on Tuesday, June 13th, as the country sweltered in a heatwave.

In contrast, average temperatures from June 1st to 15th this year at Dublin’s Phoenix Park were 12.5 degrees, down almost a degree from this May.

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Moreover, the bad news is that apart from brief respites – there is one due midweek when a warm airflow from the southwest breaks in, bringing temperatures to the early 20s – there is no longer-term promise of any sustained warm spell.

Met Éireann’s Joanna Donnelly explained the kind of weather we get is a result of the polar front jet stream, a 30,000ft (9,140m)-high air stream that forms where cold air from the Arctic meets warm air from the tropics.

The jet stream doesn’t travel in a straight line, however, and “you get loops, it goes up and down”, Ms Donnelly said.

The optimum position for sun worshippers is to have the jet stream north of us. But it is currently to the south, looping up from the south of Spain to Denmark, and anything above the loop is being hit with the colder Arctic air, while anywhere below the looping line is more influenced by warm tropical air.

The Mediterranean is therefore currently warm, Ms Donnelly said, while in Ireland we are experiencing the chill effects of being on the wrong side of the line.

“There is a good day [on] Wednesday,” Ms Donnelly said, but “there is no sign of a prolonged spell of good weather.”

Wednesday’s good weather comes to us courtesy of a southwesterly airflow that will push the northerly, polar air away. The jet stream will move to a position slightly north of us, and temperatures midweek will rise to about 22 degrees by Wednesday or Thursday.

But the longer-term outlook is not so optimistic. Ms Donnelly said in settled conditions Met Éireann can forecast for about ten days ahead but that in unsettled conditions that reliability is down to about five days.

“The jet stream might move, it tends to move, but you cannot make it move,” she said.

Ms Donnelly said for a prolonged spell of good weather we need to see the jet stream move to the north of us and stay there. “What we need is for the loops to get stuck. We call that an omega block, giving a period of prolonged high pressure.”

Tim O'Brien

Tim O'Brien

Tim O'Brien is an Irish Times journalist

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