Atmospheric precursors for intense summer rainfall over the United Kingdom

Abstract

AbstractIntense sub‐daily summer rainfall is linked to flooding impacts in the United Kingdom. Characterizing the atmospheric conditions prior to the rainfall event can improve understanding of the large‐scale mechanisms involved. The most intense sub‐daily rainfall intensity data generated from rain gauge records across the United Kingdom over the period 1979–2014 are combined with fields from the ERA Interim reanalysis to characterize atmospheric conditions prior to heavy rainfall events. The 200 most intense 3‐hourly events for six UK regions are associated with negative anomalies in sea level pressure (<−2 hPa) and 200 hPa geopotential height (<−60 m) to the west or south west of the United Kingdom 1 day earlier, with above average moisture, evaporation and dew point temperature over North West Europe. Atmospheric precursors are more intense but less coherent between regions for composites formed of the 25 heaviest rainfall events but all display substantial moisture transport from the south or south east prior to their occurrence. Composites for the heaviest events are characterized by a tripole geopotential anomaly pattern across the North Atlantic. Above average geopotential height and dew point temperature over Newfoundland and below average geopotential height but elevated evaporation in the North Atlantic are found to be weakly associated with an increased chance of the most intense sub‐daily rainfall events 5–9 days later.