Connecting atmospheric blocking to European temperature extremes in spring

Atmospheric blocking is an important contributor to European temperature variability. It can trigger cold and warm spells, which is of specific relevance in spring because vegetation is particularly vulnerable to extreme temperatures in the growing season. The spring season is investigated as transition period from predominant connections of blocking with cold spells in winter to predominant connections of blocking with warm spells in summer. Extreme temperatures are termed cold or warm spells if temperature stays outside the 10th to 90th percentile range for at least 6 consecutive days. Cold and warm spells in Europe over 1979 to 2014 are analyzed in observations from E-Obs data and the connection to blocking is examined in geopotential height fields from ERA-Interim. A highly significant link between blocking and cold and warm spells is
found which changes during spring. Blocking over the north-eastern Atlantic and
Scandinavia is correlated with the occurrence of cold spells in Europe, particularly
early in spring, while blocking over central Europe is associated with warmer
conditions, particularly from March onwards. The location of the block also impacts the spatial distribution of temperature extremes. More than 80% of cold spells in southeastern Europe occur during blocking whereas warm spells are correlated to blocking mainly in northern Europe. Over the analysis period, substantial interannual variability is found but also a decrease in cold spells and an increase in warm spells. The longterm change to a warmer climate holds the potential for even higher vulnerability to spring cold extremes.