The UK lies at a crossroads of weather systems. From the north comes the cold and dry air from the Arctic, from the west is the moist, wet air off the Atlantic, the east sends cool and damp air from continental Europe and from the south is the warm and damp air from north Africa.
All these systems are basically in conflict with one another, whichever one dominates at any particular point in time has a very strong bearing on the weather in the UK.
Into the mix comes the jet-stream. Normally in summer it lies to the north of the UK running between Scotland and Iceland, as winter approaches it migrates southward. Because the jet-stream blocks the north-south and south-north movement of air masses it acts as a barrier with cold air to the north and warmer air to the south.
The jet stream has always had a certain unpredictability about it, whilst the general direction of flow is anti-clockwise in the mid to high northerly latitudes, it regularly meanders about. In recent years it’s become ever more erratic and nowadays it’s not unusual for it to wander thousands of miles off course.
It’s also increasingly coming across another wind feature, these are Rossby Waves. These waves oppose the flow of the jet stream and can cause it to stall or deflect off course.
On top of this the Arctic weather is becoming more disrupted. Historically it always followed the same pattern. A cyclonic (low pressure) system sat over Siberia and an anticyclonic (high pressure) system was established over Canada. The air flowed from the high pressure zone to the low pressure one and created regular and predictable weather patterns.
Since 2000 this system has become unstable and on eight occasions the Arctic weather has been thrown into a complete reversal, the most obvious effect is that cold places warm up and warm places cool down.
So there’s a lot going on that influences weather in the UK.
Those events you mentioned were indeed caused by unusual movements of the jet-stream. The extensive flooding of 2007 and 2012, the cold winters of 09-10, 10-11 and 12-13, the heatwaves of 2003 and 2012, the drought of 11-12 were all influenced by the jet-steam taking an unusual path.
The most recent extreme weather event was the snow and cold temps early in the year, at that time the disruption in the Arctic together with the southerly position of the jet stream allowed cold air to flood down from the Arctic which mixed with moist air from Europe, the result being cold and snow.
Last year saw month after month of heavy rainfall coming immediately after the long drought and March heatwave. This time the jet-stream had stalled right over the UK and this allowed one weather system after another to come in off the Atlantic bringing moist air with it.
Because the jet-stream is in a constant state of flux these anomalies can last a few days, weeks or months and so, between these periods of disruption, are times when it returns to a more normal pattern; this is what the UK has at present, quite how long it will remain like this is impossible to say.
The role of the Arctic in governing global weather patterns is of vital importance. In the last few decades the amount of ice has significantly retreated, today (29 Jun 2013) there is just under 10 million km2 of ice, historically at this time of year there would have been about 13 million km2 of ice. At the end of the annual summer melt the situation is a lot worse and last year the ice retreated to it’s lowest ever extent (3,489,063km2 on 16 Sep 2012).
The ice provides a reflective surface that bounces most of the sunlight straight back into space (85% for newly formed bright ice, 55% for the dirtier multiyear ice). Once the ice melts it exposes the darker oceans which only reflect 8% of sunlight. The heat energy from the Sun warms up the oceans and in turn melts the ice even faster. The result is that the Arctic has warmed more than anywhere else.
The presence of extra heat energy in the Arctic atmosphere causes disruption to all weather patterns (heat drives every kind of weather). Exactly how it impacts on the jet stream isn’t clearly understood, there are many possible theories that are being looked at including thermal gradients, wind formation, pressure differences etc.
Whatever happens in the Arctic, the jet stream will always move north and south, it’s just that it’s becoming more erratic and less predictable.
The jet stream moves around a lot, more so in the last couple of years, you would be better off checking out the arctic oscillation whether it is in negative or positive mode to understand what is happening.
The 2012 Arctic ice melt was extreme mainly through an intense long lasting summer cyclone that broke up the ice, however in October and November there was a record refreeze and by the time the extreme cold weather set in, it was back to average (for the last ten years that is) so I did not fall for that one, the truth is the forecasters had no idea what was happening and were looking for excuses
http://ocean.dmi.dk/arctic/plots/icecove...
some think that governments move the jet streams around in a weather modification war that has been going on since the 1960's .although it was band , the can do it.
The jet stream moves around a lot every day. There is no normal position.
No, and look for even more freaky weather!
Has the Jet Stream moved back to its normal position?
Here in UK we have been told that the reason for colder winters and wet cold summers recently was the Jet Stream moving to the south of The British Isles, hence blocking any high pressure systems which would bring us settled warm and dry weather.
Now, according to this website I found at random (hope it's a good one) the jet stream has moved north and we should have fine summer weather.
http://uk.weather.com/story/news/july-outlook-2013-20130628
We were told the jet stream had moved south due to a massive melt of Arctic ice. Given that in one month the ice is unlikely to have grown back, in fact presumably melted even further, why has the jet stream moved?
Or was the arctic melting ice theory not correct?
Confused to say the least, please explain why less ice makes the jet stream move south, even lesser ice makes the jet stream move north again.
http://phys.org/news/2012-09-loss-arctic-ice-trigger-extreme.html#inlRlv
http://uk.weather.com/story/news/july-outlook-2013-20130628
