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SACRUS

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    The Allsnow Blizzard of 2026

    in New York City Metro

    Posted

    What it is: The National Blend of Models (NBM) is NOAA/NWS’s statistically post-processed blend that combines dozens of deterministic and ensemble models into a single, calibrated forecast grid used operationally across the U.S.

    Models included: Core inputs typically include GFS, GEFS, ECMWF (Euro), ECMWF ensembles, NAM (12 km & 3 km), HRRR, RAP, CMC/GEM, UKMET, and select regional ensembles (availability varies by cycle and variable).

    Weighting approach: Dynamic, variable-specific weighting is applied—models are weighted differently by forecast hour, parameter (QPF, snow, wind, temp), season, region, and recent skill, rather than a fixed average.

    Post-processing & bias correction: Raw model output is statistically bias-corrected, smoothed, and calibrated using historical verification, climatology, and consistency checks to reduce noise, outliers, and known model biases.

    Operational output: Produces probabilistic and deterministic fields (means, percentiles, PoPs, snowfall ranges) and serves as the baseline guidance for NWS forecast grids, with human forecasters adjusting for mesoscale and event-specific factors.

    • Like 3

    The Allsnow Blizzard of 2026

    in New York City Metro

    Posted

    4 hours ago, SACRUS said:


    2/21 18z Summary

     

    Total QPF NYC 
    /
    Snow 10:1 NYC


    SREF: 2.1 / 19.6
    NAM:  2.8 / 27.6
    NAM 3K:  2.2 / 21.6
    ICON: 1.3 / 12.9
    RGEM: 1.1 / 11
    GFS: 1.7 / 17.1
    GFS AI AIGFS:  1.3 / 12.7
    UKMET: 1.7 . 15.2
    GEFS Mean : 1.8 / 18.2
    Euro: 1.3 / 11.1
    Euro AI AIFS: 1.2 / 11.4



    SREF: 2.1 / 19.6
    NAM:  2.8 / 27.6
    NAM 3K:  2.2 / 21.6
    ICON: 1.3 / 12.9
    RGEM: 1.1 / 11
    GFS: 1.7 / 17.1
    GFS AI AIGFS:  1.3 / 12.7
    UKMET: 1.7 . 15.2
    GEFS Mean : 1.8 / 18.2
    Euro: 1.3 / 11.1
    Euro AI AIFS: 1.2 / 11.4

     

    Mean Total QPF (NYC): 1.68 inches

    Mean 10:1 Snowfall (NYC): 16.2 inches

    • Like 1
    • Thanks 3

    The Allsnow Blizzard of 2026

    in New York City Metro

    Posted

    4 hours ago, SACRUS said:


    2/21 18z Summary

     

    Total QPF NYC 
    /
    Snow 10:1 NYC


    SREF: 2.1 / 19.6
    NAM:  2.8 / 27.6
    NAM 3K:  2.2 / 21.6
    ICON: 1.3 / 12.9
    RGEM: 1.1 / 11
    GFS: 1.7 / 17.1
    GFS AI AIGFS:  1.3 / 12.7
    UKMET: 1.7 . 15.2
    GEFS Mean : 1.8 / 18.2


    Updated with GEFS mean(s)

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