The climatology and nature of warm-season convective cells in cold-frontal environments over Germany

Abstract

Abstract. Cold fronts provide an environment particularly favourable for convective initiation in the mid-latitudes and can also be associated with convective hazards such as wind, rain and hail. We build a climatology of cold-frontal convective cells between 2007–2016 for April–September in a cell-front distance framework by combining a radar-based cell detection and tracking dataset and automatic front detection methods applied to reanalysis data. We find that on average around twice as many cells develop on cold-frontal cell days compared to non-cold-frontal cell days. Using the 700 hPa level as a reference point we show the maximum cell frequency is 350–400 km ahead of the 700 hPa front which is marginally ahead of the mean surface front location. The 700 hPa front location marks the minimum cell frequency and a clear shift in regime between cells with a weakened diurnal cycle on the warm-side of the 700 hPa cold front and strongly diurnally driven cells on the cold-side of the 700 hPa front. High cell frequencies are found several hundreds of kilometres ahead of the surface front and cells in this region are most likely to be associated with mesocyclones, intense convective cores and lightning. These results are an important step towards a better understanding of cold-frontal convection climatology and links between cold fronts and convective hazards.