The GPM Ground Validation Advanced Microwave Precipitation Radiometer (AMPR) OLYMPEX dataset was collected by the AMPR instrument flown on the high altitude ER-2 research aircraft from November 9 - December 15, 2015, during the Olympic Mountains Experiment (OLYMPEX) field campaign conducted at Washington State’s Olympic Peninsula. AMPR is an airborne passive microwave radiometer from which cloud, precipitation, water vapor, wind speed and wind direction can be obtained using advanced algorithms with the 10.7, 19.35, 37.1, and 85.5 GHz microwave frequency brightness temperatures measured by AMPR. The primary goal of OLYMPEX was to validate rain and snow measurements in midlatitude frontal systems moving from ocean to coast to mountains. AMPR data at the Global Hydrology Resource Center (GHRC) DAAC include netCDF format data files of brightness temperature and PNG browse files of Quality Control Flags and Brightness Temperatures.