Non-Standard Blockage Mitigation for National Radar QPE Products

Severe terrain blockages, inaccurate blockage information and anomalous propagation of the electromagnetic waves lead to discontinuities and artificial gaps in radar reflectivity fields and subsequently the radar-derived quantitative precipitation estimation (QPE) field. This problem can become very pronounced in the accumulated QPE products and causes inaccurate hydrological predictions.

To mitigate such discontinuities and to produce a physically continuous depiction of precipitation, a “Non-Standard” Blockage Mitigation (NSBM) scheme was developed for the WSR-88D radar network. Firstly, azimuthal gaps were identified subjectively by experienced radar meteorologists from QPE accumulations and a NSBM table is created for each radar and for each Volume Coverage Pattern. Based on the size and severity of any given azimuthal gap, one of the following actions is applied to the hybrid scan precipitation rate field: 1) cross-azimuth interpolation; 2) replacing current data with those from the higher tilt; 3) apply azimuthal or radial smoothing across tilt boundaries. The approach has been implemented in a real-time national multi-radar, multi-sensor system that integrates over 130 radars for 7 years and was shown to be very effective in alleviating/removing various blockage discontinuous in the national precipitation products.