To create the PQPF guidance, WPC combines the deterministic WPC QPF guidance with the QPF distribution from a multi-model ensemble. PQPF percentile grids and a grid which describes the distribution spread are sent to WFOs who may then adjust the probability distribution based on the local WFO QPF forecast. The final 10th and 90th percentile grids are used to represent the best case scenario and reasonable worst case scenario respectively, with the local office storm total QPF grid representing the most likely scenario. Graphics of these three grids are available internally to each participating office for evaluation along with verification statistics generated within the GFE.
This work presents a detailed description of the project, the methodology, and a preliminary assessment and verification of PQPF guidance at some of the participating pilot offices. Performance trends are also assessed in relation to biases observed towards differing precipitable water regimes and convectively-driven environments. An application utilizing PQPF guidance in a decision support services framework is also presented. Finally, improvements to the methodology using statistical calibration techniques to improve the distribution functions, expansion of participating offices, and availability of guidance for public feedback will be explored as part of the PQPF experiment in the future.