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Summer update

Looking promising?


15/06/2017

The TWO seasonal forecast issued in late May suggested a warm summer with a dry second half. June was expected to be mixed and that has proven to be the case so far. Large parts of the UK have already had over 90% of their monthly rainfall. Despite the wet start the Central England Temperature (CET) is provisionally 1.4C above average to June 14th. How are things shaping up in the medium term? 

Warmer than average outlook?

Medium range ensemble models are pointing towards above average temperatures. The next 10 days look predominantly very warm or hot for much of the country. During the last week of June the expectation is for lower temperatures and an increased risk of rain.  The chart for London below illustrates this. The top half shows forecast 850hPa temperatures for the next 16 days and the lower half represents rainfall. The key points are:

1) Most of the ensemble runs keep 850hPa temperatures at or above 10C until June 23rd. (850hPa is about 1500m above sea level, and 10C suggests daytime temperatures around 25C at the surface)

2) The number of runs showing showers / rain increases significantly during the last week of the month 

GEFS 16 day probability forecast

Long range outlook

The medium range data ends on a more mixed note with cooler and wetter conditions. Does this set the scene for the rest of summer? Probably not if the latest GloSea5 seasonal model output is correct. It favours warmer and drier than average conditions during July and August. Therefore our expectation for the rest of the season continues to be in line with the TWO seasonal forecast.

Summary

Medium and long term forecast models suggest above average temperatures over the period as a whole but cooler interludes are probable. Wetter spells are also expected but over the rest of the summer a good deal of dry weather is considered likely.

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