Summer Weather

One of the reasons for the lack of trip reports has been the appalling weather. It was exactly two years ago that we had the driest Spring for 80 years, see previous post on the local reservoirs.

The last of the hosepipe bans in the southeastern corner of England were lifted a couple of weeks ago, and not before time. Normally the water year begins in October, when the reservoirs and water-bearing rocks beneath our feet begin to fill up again after the summer. Since March 2012 we have had an excess of 220mm of rainfall and the reservoirs are full.

It has all been the fault of the mid-latitude jet stream, that powerful conveyor belt of winds in the upper atmosphere.

The jet stream is located in the zone of biggest temperature contrast. These huge temperature contrasts (between the Artic and Equator) provide the energy which drives this narrow stream of powerful winds. The jet stream also controls the behaviour of the depressions that we see on the TV weather charts, and these depressions routinely bring widespread rain, and often strong winds.

Throughout the 1990s and the early-2000s the jet stream blew powerfully from the west, and the distribution of weather across the UK was relatively normal, with just a few exceptional droughts and wet periods. Since 2003, however, the flow has been sluggish and meandering, and as a result we have experienced long periods when the weather has appeared to get stuck in a rut. So we had heat-wave summers in 2003 and 2006, appalling floods in 2007 and now in 2012, and an extended drought in 2010 and 2011.

It seems that the six-week long period of thick cloud and heavy rain may be drawing to a close. The weather should take a turn towards something rather drier, sunnier and warmer.

The last time the Olympics came to London, in 1948, we had a dreadful summer, apart from two weeks at the end of July. King George VI opened the Olympic Games on the hottest day of the year with 35C (95F) approached in London and the Home Counties. But sadly that year the rains returned in August.