Case Study of Orographic Precipitation within Measurement Gaps of Satellite-based Precipitation Products

The spatial and temporal variability of rainfall over mountainous regions remains challenging to capture from ground-based observations globally due to terrain complexity. This promotes integrated satellite-based precipitation products (SPP) with quasi-global coverage. The Integrated Multi-Satellite Retrievals for GPM (IMERG) algorithm intercalibrates, merges and interpolates all available passive microwave (PMW) retrievals, microwave-calibrated infrared (IR) satellite estimates, and rain gauges. Yet, multiple uncertainties are associated even with Level-2 PMW data. Specifically, PMW sensors have gaps in coverage and their retrievals depend on an ice phase aloft. In this study early synoptic indicators of the likelihood of orographic precipitation occurring within the PMW measurement gaps will be explored. With the use of measured and modelled data from the Weather Research & Forecasting Model (WRF), this work performs a case-study analysis of an event of shallow convection captured during the OLYMPEX field campaign (2015) with the aim to understand performance of PMW retrievals by identifying the synoptic predictors present for this case of shallow convection in the Olympic Mountains. Furthermore, instrument gaps in coverage in mountainous regions are cataloged and synoptic/environmental predictors likely to be present for events falling within these gaps are speculated.