NBM v4.3 upgrade goes live May 20, 2025

On April 15, 2025, NOAA/NWS issued a service change notice for NBM v4.3, scheduled to become operational on May 20, 2025, starting with the 12Z cycle. If a Critical Weather Day occurs, the implementation could be delayed.

About NBM

The National Blend of Models (NBM) is NOAA's flagship post-processing system that blends guidance from multiple models (global, regional, deterministic, and ensemble) into a single, calibrated dataset. It delivers both deterministic and probabilistic fields with hourly updates and high spatial resolution, making it the backbone for many downstream forecast products.

Key changes in v4.3

• Tropical cyclone wind products use a feature-matching approach to improve storm tracking and wind placement.
• SPC probabilistic severe guidance receives updates to align with ongoing product changes.

The upgrade affects the CONUS and all OCONUS domains (Alaska, Hawaii, Puerto Rico, Guam, Oceanic).

Why it matters

Model upgrades can introduce step changes in time series and verification baselines. If you run long backtests, consider:

• Splitting evaluation windows before/after May 20, 2025.
• Recalibrating thresholds for wind or severe-weather products.
• Annotating model-version changes in downstream analytics.

What this means for GribStream users

GribStream already supports NBM. We will continue to track NOAA upgrades and align our feeds as updated data are published through the AWS Open Data program.

Sources

• NWS Service Change Notice 25-34 (Apr 15, 2025): https://www.weather.gov/media/notification/pdf_2025/scn25-34_upgradeNBM_V4.3.pdf