Reply #3: It was expained fully

[dipsydoodle]

on one of UK TV News weather segments a few days back.

I just searched and found this expanation here :


It now seems that these two apparently disconnected events have a common cause. They are linked to the heatwave that killed more than 60 in Japan, and the end of the warm spell in western Europe. The unusual weather in the US and Canada last month also has a similar cause.

According to meteorologists monitoring the atmosphere above the northern hemisphere, unusual holding patterns in the jet stream are to blame. As a result, weather systems sat still. Temperatures rocketed and rainfall reached extremes.

Renowned for its influence on European and Asian weather, the jet stream flows between 7 and 12 kilometres above ground. In its basic form it is a current of fast-moving air that bobs north and south as it rushes around the globe from west to east. Its wave-like shape is caused by Rossby waves – powerful spinning wind currents that push the jet stream alternately north and south like a giant game of pinball.

In recent weeks, meteorologists have noticed a change in the jet stream's normal pattern. Its waves normally shift east, dragging weather systems along with it. But in mid-July they ground to a halt, says Mike Blackburn of the University of Reading, UK (see diagram). There was a similar pattern over the US in late June.

http://www.newscientist.com/article/mg20727730.101-frozen-jet-stream-links-pakistan-floods-russian-fires.html

Its a shame there isn't a picture. Draw a sine wave and then imagine pushing the ends together as though to increase the frequency - would push the peaks higher at the same time. That's the current shape as opposed to normal and why the hot air is reaching Russia.