Persistence and orographic modulation of mesoscale precipitation areas in a potentially unstable warm sector

Abstract

Abstract In this paper we use data from radars and raingauges in England, Wales and southern Ireland to study the motion and changes in intensity of mesoscale precipitation areas (MPAs) some tens of kilometres across as they traversed two regions of high land and an intervening stretch of sea. The MPAs studied were associated with an area of middle‐level potential instability within a windy and moist wintertime warm sector, a situation known to produce major orographic effects. Despite the very large modulation of the rainfall intensity by orography, it was found that most of the MPAs could be tracked for 6h over a distance of 600 km, all the way from the west coast of Ireland to southern England. The implications of this are discussed with regard to the use of radar and satellite data in short‐period forecasting.