Atmospheric River Hazard Tool

Operational Forecast
Historical Cases

Supported by the National Science Foundation Coastlines and People Program: #2052972

Model Climate: How does this forecast compare to past forecasts with similar lead time?

Plot description: Model Climate (M-Climate) is generated based on NOAA’s Global Ensemble Forecast System, version 12 (GEFSv12) reforecast data (2000-2019), for integrated water vapor transport (IVT), freezing level (Z0), 1000-hPa wind (UV), and Quantitative Precipitation Forecasts (QPF) (shading, percentile rank). This places important forecast elements in the context of reforecasts with the same lead time and at similar times of year. For example, large M-Climate Percentile Rank IVT values indicate GEFS ensemble mean IVT values are large for a given lead time. The contours show the ensemble mean forecast IVT (kg m-1 s-1), freezing level (feet), 1000-hPa wind (knots), and QPF (mm 3-hr-1) based on NOAA’s Global Ensemble Forecast System. The AR Hazard Index summarizes grid-level conditions by assigning scores (1–5) based on extreme M-Climate percentiles of IVT, freezing level, wind, and QPF. Additional points are given for prolonged IVT extremes and wind/IVT orientations perpendicular to topography (see below for a detailed breakdown of the AR Hazard Index). The image on the right shows the potential hazards that could be messaged based on the AR Hazard Index that could impact people and infrastructure.

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AR Hazard Index scoring

  • IVT
    • +0.5 if > 95th percentile
    • +0.5 if > 98th percentile
    • +0.5 if > 95th percentile for 24 consecutive hours
    • +0.5 if > 95th percentile for 48 consecutive hours
    • (Maximum for IVT: 2.0 points)
  • Freezing level
    • +1.0 if > 95th percentile and initialization date is between Oct 15 – May 1
    • (Maximum for freezing level: 1.0 point)
  • 1000-hPa wind
    • +0.5 if > 95th percentile
    • (Maximum for 1000-hPa wind: 0.5 point)
  • QPF
    • +0.5 if > 95th percentile
    • +0.5 if > 98th percentile
    • (Maximum for QPF: 1.0 point)
  • Direction (IVT or 1000-hPa wind)
    • +0.5 if direction is perpendicular to topography (IVT OR 1000-hPa wind)
    • (Maximum for direction: 1.0 point)

Total maximum AR Hazard Index score: 5.5 points

Data Sources

  • National Centers for Environmental Prediction (NCEP) Global Ensemble Forecast System (GFS) Model obtained from NOAA/NCEP at 0.5-degree resolution via NOMADS.
  • The NOAA GEFS Reforecast version 12 data at 0.25-degree resolution was obtained from NOAA via Amazon AWS.