Much discussion around the current floods has focused on predicting what rain is coming and where, but that still leaves the question of why it has been unrelentingly wet in the usually drier eastern half of the country.
For an answer to that, we have to look far above and beyond the clouds overhead.
It’s about “clashes” and “battlegrounds” says Paul Moore, climatologist with Met Éireann, as the many forces that shape our weather collide and get knocked out of shape.
High above – in both latitude and altitude – is the polar vortex, a wide band of cold air dozens of kilometres up that swirls around in alternating westerly and easterly directions.
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When it’s in its easterly phase, as it is at the moment, it tends to be weaker.
“It’s more prone to disruption and it wobbles and stretches,” says Moore.
“It has stretched into North America and enabled a cold air mass to come down from the Arctic.”
Much of Canada and the US has been snowbound and freezing as a result but there is a knock-on effect for us as it pushes lots of extra-cold air out into the Atlantic.
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Jet streams, other bands of air or “rivers of air” also flow continuously around the earth.
The one influencing Ireland picks up whatever is the prevailing air mass coming across the Atlantic.
It’s often mild – influenced by warm air moving upwards from the Caribbean and the gulf stream – and sometimes wild when the warm air from those places is full of hurricane-fuelled fury.
At the moment, the dominance of warm air is being challenged by the cold air being pushed down by the polar vortex.
“That clash between the warm air and the cold has fired up the jet stream coming across the Atlantic,” says Moore.
“It’s moving faster and picking up the low-pressure systems [associated with higher rainfall] on the approach to Europe.
“At the same time, it’s being displaced to the south because there are high pressure systems to our north and east.
“That’s why the rain is coming from the south and affecting the east and southeast.
“We’re in the battleground between the warm air from the south and the cold air from the east.
“This high pressure is very cold dense air and it’s blocking the systems moving up from the south so that they are stalled and the rain can’t clear away.”
The UK Met Office has a similar explanation for its similarly sodden citizens.
“Cold plunges across North America have helped to strengthen the jet stream,” it said.
“As that cold, dense air moves southwards, it enhances the temperature contrast between warm and cold regions – one of the key factors that energises the jet.
“A stronger jet stream acts a bit like a conveyor belt, rapidly developing and then propelling areas of low pressure towards northwest Europe.
“At the same time, high pressure has also established over parts of northern Europe.
“This has created a ‘blocked’ pattern, preventing any significant shift in the position of the jet stream and limiting our chances of more settled, drier weather developing.”
So just how limited are the chances of a return to somewhat normal conditions?
The UK Met Office is cautious. “When the atmosphere becomes stuck in this sort of regime, it can take time for the large-scale pattern to reset,” it said.
Moore expects a break over the weekend but warns that even if the jet stream begins to shift back north, it will still bring normal February rains, just with less concentration on the east and southeast.
