Jet Stream Winter Blues

The one thingthat we have learned is that the jet stream is able to hugely divert weatherconditions anywhere but certainly over North America.  We have been experiencing an extreme of thejet stream.  Most winters it largelystays put.  Most of the time it variesvery little over a known channel.  Theproblems occur when it decides to go a little crazy like this winter.

The netglobal heat may vary little from year to year, but it is no fun to find thatArctic conditions have moved south while the Arcticwarms up.

This wintergot hard and difficult from the beginning and has sustained it throughout.  I have no doubt that dying flocks of birdsrepresent the fatal exhaustion of large numbers of birds trying to maintaintheir position in suddenly declining conditions.  The cold has simply lasted too long.

By now weshould have had a break in the weather allowing recovery.

How a freak diversion of the jet stream isparalysing the globe with freezing conditions

Last updated at 12:53 PM on 22nd December 2010

It's snowing in Australiaand California yet 'warm' in Greenland

Thefreezing conditions that have blasted Britainare being blamed on a series of weather patterns that are bringing Arctictemperatures to much of western Europe, Californiaand even Australia.

One ofthe main factors is a change in the position of the jet stream - thefast-moving current of air that moves from west to east, high in theatmosphere.

Changes inthe jet stream's path can cause massive changes in weather conditions acrossthe globe and may be why Australians are now shivering their way through summerand the current freezing conditions in California.

In anormal British winter - when conditions are mild and soggy - the jet streamlies over northern Europe, at an altitude ofbetween 35,000 to 50,000 feet.

Dailymean temperature anomalies around the world between 1st December and 20thDecember compared with the 30 year long term average between 1961 and 1990

Duringthese grey winters, Britain'sprevailing winds come from the west and south west, and bring with them warmand moist air from the sub-tropical Atlantic.

Thisyear a high-pressure weather system over the Atlantic is blocking the jetstream’s normal path and forcing it to the north and south of Europe.

Theareas of high pressure act like stones in a stream - blocking the normal flowof milder air from the west and instead forcing colder air from the north downacross the UK.
In California more than 12 inches of rain has fallen inparts of the Santa Monica Mountains in the south and 13 feet of snow hasaccumulated at Mammoth Mountain ski resort.

AndAustralians expecting to bask in early summer sun this Christmas are insteadshivering as icy gusts sweeping up from the Southern Ocean have blanketed partsof east coast states New South Wales and Victoria with up to four inches ofsnow.

When thejet-stream is blocked by high pressure it dips southwards and lets freezing airflood in from the Arctic regions.

Otherweather patterns are also causing havoc across the may also be affecting theweather, such as the current in the tropical Pacific Ocean, called La Nina,which is disturbing the jetstream over the north Pacific and North America.

Acombination of our usual wet Atlantic weather systems striking these freezingcold fronts results in huge amounts of snowfall – and brings Britaingrinding to a halt.

A MetOffice spokesman: ‘The problem is we are not getting the warmer Atlantic airthat normally keeps our winters mild.’

‘We cansee that it is unseasonably warm over Canadaand Greenland, this is where warm air has beendiverted.’

He saidthat any change in the pressure over the Atlantic would need to last forseveral days before we would notice any change in the weather in Europe.

Freezing-coldwinters and milder winters tend to cluster in groups, as the jet stream changesits path. 

Expertsare still unsure why this is but suspect it may be related to the EL Ninoweather system as well as changes in sea temperatures and solar activity.

A system of high pressure has forced the jetstream further south, allowing biting cold winds in from the north

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