Upland rainfall is changing but regional climate models (RCMs) are poor at simulating observed precipitation in such areas of complex topography. This paper presents a method of examining observed rainfall patterns and processes under different conditions of synoptic meteorology and local topography. Objective topographic descriptors are defined and used to distinguish the modification of rainfall by local topography from that due to different synoptic conditions and climate change. A case study examining winter rainfall in Cumbria is presented. The conditional analysis method can be used to test RCM outputs so that model parameterisation can be improved.