Verification of Probability of Precipitation in the National Blend of Models
Tabitha Huntemann, NOAA/NWS Meteorological Development Laboratory, Silver Spring, MD
David Ruth, NOAA/National Weather Service, Meteorological Development Laboratory

The National Weather Service (NWS) is developing the National Blend of Models (NBM) to provide a nationally consistent and skillful suite of calibrated forecast guidance based on a blend of NWS and non-NWS deterministic, ensemble, and statistically post-processed model output. The NBM contains blended guidance for many National Digital Forecast Database (NDFD) elements over the conterminous United States (CONUS), Alaska, Hawaii, and Puerto Rico. The NBM is intended to serve as valuable guidance for NWS forecasters at local Weather Forecast Offices (WFOs) and national centers.

The National Digital Forecast Database (NDFD) contains official NWS forecasts produced by NWS forecasters on a fine-resolution grid. The Meteorological Development Laboratory (MDL) routinely evaluates the NDFD and compares the skill of the human forecast to guidance for the same weather element. This guidance includes the NBM, as well as Weather Prediction Center (WPC) forecasts, model forecast grids, and statistically post-processed model output.

Precipitation Potential Index (PPI) supports the generation of NDFD 12-h Probability of Precipitation (PoP12) forecasts and categorical information in the NDFD Weather grids. PPI values range from 0 to 100 and resemble PoP12 values in magnitude. The PoP12 for any 12-hour period can be derived by taking the maximum PPI value within the desired period. PPI will be available in NBM v3.0 as guidance to NDFD forecasters and will be used in NBM v4.0 as an input to NBM Weather grids.

In this presentation, we review the performance of PoP12 and PPI forecast guidance from NBM compared to WPC and NDFD forecasts for forecast periods out to seven days in advance. We will also look at any improvements to the NBM resulting from recent upgrades.