The “beast from the east” cold of late winter 2018 and the arid heat of the UK’s summer so far, are united by one pronounced meteorological phenomenon: atmospheric blocking. Large meanders in the jet stream often lead to the development of huge anticyclones – areas of high pressure that can remain stationary for weeks at a time.
A blocking area of high pressure, sitting over Scandinavia and western Russia in February and early March, maintained a static weather pattern and pulled in a conveyor of sub-zero air to the UK. Just four months later, blocking allowed high pressure to settle close to the UK. This has resulted in very warm and extremely dry conditions with some central and southern parts of the UK seeing no measurable rain for over a month.
Predicting when and where atmospheric blocking will take place is difficult, although there are some clues. One signal is solar activity, the levels of radiation, sunspots and other solar phenomena that ebb and flow on a periodic 11-year cycle. Studies have shown that, on average, a decrease in solar activity can promote an increase in atmospheric blocking, although the relationship is complex.