Overview of National Blend of Models Version 3.1. Part I: Capabilities and an Outlook for Future Upgrades

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. NBM version 3.0 (NBM V3.0) was placed into operations in July 2017 at the National Centers for Environmental Prediction (NCEP). This gridded guidance (with over 30 weather elements) has five domains including the CONUS, Alaska, Hawaii, Puerto Rico, and a large Oceanic Domain that covers much of the Pacific and Atlantic Oceans. It runs hourly (24 times per day) on the Weather and Climate Operational Supercomputing System (WCOSS). The number of model and statistically post-processed inputs roughly tripled to 12-15 for the four CONUS and OCONUS sectors.

NBM V3.0 has 1-h temporal resolution through 36 hours, 3-h from 39 to 192 hours, and 6-h from 198 to 264 hours. For the CONUS, this includes hourly resolution of Precipitation Potential Index (PPI) and 1-h QPF through 36 hours. The CONUS also has hourly ceiling height, surface visibility, and lowest cloud base through 36 hours, and these will be added to OCONUS in NBM V3.1.

Probability of Precipitation (PoP12) and Quantitative Precipitation Forecasts (QPF06) leverage quantile mapping and dressing (Hamill et al, 2016) with a 62-member ensemble. The NBM V3.0 model components include the Global Forecast System (GFS), the Environment Canada Global Deterministic Prediction System, the North American Ensemble Forecast System (NAEFS) which includes the NCEP Global Ensemble Forecast System and the Environment Canada Global Ensemble Prediction System, and the 20-member Navy Global Environmental Model (NAVGEM) ensemble (Navy’s Fleet Numerical Meteorology and Oceanography Center). Work is currently in progress to use short term, higher resolution guidance in the quantile mapping and dressing technique for NBM V3.1.

A variety of weather grid inputs to the NDFD weather grid are also produced to help predict complex winter weather precipitation types. NBM V3.1 will add 1-h and 6-h snow and ice amount forecasts. A total of 13 parameters leveraging top down methodology for determination of snow, sleet, freezing rain, freezing drizzle, and rain will be provided. In collaboration with the Storm Prediction Center, calibrated 3-h thunderstorm probabilities are included through 87 hours, along with 6-h gridded GFS MOS probability guidance of thunder from 90 to 192 hours.

NBM V3.1 improves the science and statistical post-processing of current elements, adding more Numerical Weather Prediction (NWP) and previous runs of NWP (time lags). Of greater importance is covering service gaps to the aviation, marine, and fire weather programs. This includes but is not limited to low level wind shear, echo tops, significant wave heights, Haines index, and mixing heights.