Monsoon weather could mean a total washout this summer
Northern Ireland remains in the grip of a 'European monsoon' — but it looks like it could lift for the Twelfth, albeit temporarily.
The little known phenomenon is partly responsible for the latest wash-out summer and some forecasters are predicting that 2008 could be among the top five wettest summers on record.
The unsettled weather, which has sparked a number of severe weather warnings across the UK by the Met Office, is believed to be linked to the position of the jetstream which is currently further south than is normal for this time of year.
Michael Dukes of forecasters MeteoGroup UK said the European monsoon is the name given to an early summer weather feature.
It has always been around but is more evident in some years than others.
Westerly winds predominate over the winter, bringing wet stormy weather in from the Atlantic Ocean, but tend to be superseded in spring when others winds come into play, he said.
"Then during June the westerly winds start to come in heavily and bring the Atlantic weather systems back in," he said.
"It's often called the return of the Westerlies or the European monsoon — it happens in most years — but in some years it is more evident than others. It's the moist westerly winds that are most common in Northern Ireland.
"What you hope is that they don't keep blowing through the whole of the summer. In some years they blow for a few weeks and then disappear again. Some years they just keep on blowing — like last year."
Michael said the long range forecast is inaccurate at the best of times, so only the next week or so can be forecast with any confidence.
"We've just got more unsettled weather coming, but there are hints that the second half of July will be a little better. But in the next couple of weeks there is no sign of any prolonged blue skies and hot sunshine," he said.
The European monsoon has always been around and has nothing to do with global warming, he said.
However, climatologists expect south eastern Britain to become hotter and drier under climate change.
While Northern Ireland may become warmer in summer, its climate is also expected to remain moist.
But while the weather is predicted to remain unsettled for the next few weeks, it looks as though Northern Ireland could escape most of Saturday's showers during the Twelfth celebrations this Saturday.
Sunshine and scattered showers are predicted for Thursday and Friday.
What is a European monsoon?
JET streams are narrow fast-flowing rivers of air, formed by temperature differences in the upper atmosphere between the cold polar air and the warm tropical air. The abrupt change in temperature causes a large pressure difference which forces the air to move.
They're typically thousands of miles long, hundreds of miles and a few miles deep, speeding along at up to 300 miles an hour. It's thought that the rain-bearing depressions that invade the UK from the Atlantic begin forming around the jet streams and percolate downwards.
The position of the jet stream is thought to be linked to the June rains that often return to the UK in full force just when it looks like a balmy summer is on the cards. The phenomenon is dubbed the European Monsoon or the Return of the Westerlies — the Atlantic winds that bring stormy weather in winter.