In meteorology, the term blocking is used to describe a situation where areas of relatively immobile high atmospheric pressure (anticyclones) tend to dominate weather patterns for many days.
Over the UK, blocking situations are typically associated with relatively cold, still conditions often accompanied by fog in winter, and dry sunny conditions and heatwaves in summer. The hot summer of 2003 and the cold winter of 2009/10 were both associated with blocking.
The mechanisms for atmospheric blocking are only partially understood, and the prediction of the intensity and duration of blocking events is one of the most difficult weather forecasting situations.
- UKCP09 provides a commentary about potential future changes in blocking over the UK in Annex 6 of the UKCP09 Climate change projections report. Blocking is also discussed, in terms of assessing how well HadRM3 (the regional climate model, RCM, used in UKCP09) simulates large-scale atmospheric features, in Annex 3.4.2.
- Information about past blocking anticyclones in the UK is available from the UKCP09 Extremes atlas.