Monday 10 June 2013, 16:05
An expected return to more changeable weather through this week reminded me of the work of one of our best known and most respected climatologists Professor Hubert Lamb.
Professor Lamb is credited with discovering an empirical relationship between low solar activity and an increased probability of higher pressure in winter across more northern latitudes – which leads to colder winters across the UK and Europe.
Another part of his work was to analyse weather patterns over 100 years to try and see if any repeat themselves across the UK, with some success.
One of his main findings was a change of pattern from around the middle of June, which, in his words, saw the ‘return of the westerlies’.
By looking at climate data he discovered, more often than not, the Atlantic would re-assert itself around or just after mid-June, bringing changeable weather once more across our shores.
This would follow a period when westerly winds were at their weakest.
Climatologically this period is now called the ‘European monsoon’ as areas of low pressure move in from the west.
If the jet stream is behaving normally, this would mean wettest conditions in the north and west, with the least rainfall in the south and east.
Most of the time, but not always and hence the difficulty of using this as a long range forecasting tool, this changeable spell of weather would last well into July.
Lamb then discovered a second period in the climate records which tended to assert itself from mid to late July, which he called ‘thundery and cyclonic’ – in other words, less windy, warmer but with a risk of heavy showers.
This type of weather would then last well into August.
Lamb’s work effectively describes a typical British summer; one in which long spells of fine settled weather are the exception rather than the rule.
Although it’s early days, there are already indications that this summer is starting to resemble one of Professor Lamb’s typical British summers.
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