Operational Strengths and Challenges for the New Dual-Pol MRMS QPE on a Real-Time System

A new Multi-Radar-Multi-Sensor (MRMS) Dual Pol quantitative precipitation estimate (QPE) product (Q3DP), that estimates precipitation via specific attenuation (A) below the melting layer, reflectivity (Z) within and above the melting layer and specific differential phase (KDP) where rain is mixed with hail, has been integrated into the MRMS real-time research testbed. The new QPE technique is undergoing an extensive evaluation across the entire US. During this period, we have noted some of the operational strengths as well as challenges of this new QPE algorithm. In general, the new algorithm does perform better in areas where partial blockage is occurring that is typically found with the operational Dual Pol data. It also does quite well for both continental and tropical like rainfall regimes across the US. Further, it does not appear to be as vulnerable to calibration errors of Z and differential reflectivity ZDR as the rain estimation techniques utilizing those variables. However, there are some operational challenges: 1) there appears to be an overestimate bias trend in deep convection; 2) in light rainfall events, the algorithm tends to underestimate rainfall. Case analysis has shown that challenge 1) may at times be related to ice contamination but at other times it appears to be related to the application of a single parameter α (the net ratio A/KDP along the propagation path) value across the entire radar field of view when a mixture of stratiform and convective rain regimes are present. The choice of the parameter α is crucial for the accurate estimation of the specific attenuation A. In the case of the former (latter), a higher (lower) value of α may be more applicable due to the different microphysics involved in forming the two types of precipitation. These analyses have spawned new ideas into developing techniques for addressing these challenges which will be discussed.