UK Seasonal Forecast [Summer 2009] =>

*Free Guide* on: Seasonal Forecasting in the 21st Century

Forecast Valid: 1st June - 31st Aug 2009

Forecast Issued: 1st May, 2009 [20:46UTC]

- Evidence for a warm-dry summer for southern UK regions [The summer is likely to be less humid than many other warm summers experienced by the residents of the United Kingdom. Night-time minimum temperatures are likely to fall in the near-average category even within the majority of warmer periods. A cooler westerly wind will persist for many northern parts of the UK. At times a southerly flow will bring exceptionally hot conditions to Southern England.]

• The mean latitude of Polar Jet Stream which "drives" the weather system into Western Europe is further north than both the Summers of 2007 and 2008. This is a strong signal that the "Azores" High pressure system is likely to be positioned slightly further north. The Azores high is responsible for clear and sunny conditions weather conditions in the UK, particularly during the late Spring to early Autumn. The positioning of the Azores high during summer 2009 will tend to lead to hot and dry weather for the Mediterranean regions where a semi-permanent subtropical high is likely to give well-above temperatures for many parts.
  
• The North Atlantic Oscillation (NAO) is a measure of the north-south pressure difference in the north-Atlantic. When the pressure difference between the Azores and Iceland is high the "driving" of the westerly flow is enhanced. The developing pattern indicates a tendency towards a positive phase this summer. This pattern signals a drier summer for the south, but a near-normal or changeable summer further north.
  
• The activity in the jet stream and activity in the Atlantic tends to indicate that the north-west, particularly Scotland could experience a damp or changeable summer. Although in the south of the UK and particularly the south-east it seems like this season could be a bumper BBQ season.
• The general flow trajectory is west to north-west, leading to the prognosis of a "showery" or thundery breakdown to some hot-spells producing localised heavy rainfall at times for the UK, though any general synoptic rainfall approaching from the West is likely to be minimal or below the average activity, due to a domination of a blocking high.

• Overall the evidence supports 

1. England/Wales: Temperatures above average to well-above average especially in the SE quarter. Rainfall below average to well-below average.
2. Scotland and Northern Ireland: Temperatures in the near-normal category or slightly above. Rainfall above average to close to average.