Atmospheric River Scale Forecast Products

The AR scale is determined based on the duration of AR conditions (IVT >250 kg m-1 s-1) and maximum IVT during the AR as described in Ralph et al. 2019. For a description of the AR Scale view the video below.

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Ensemble Forecast Systems

Due to server maintenance at CW3E several of the EMCWF ensemble forecast products will be unavailable for several days. We apologize for the inconvenience and will update products as soon as possible.

Coastal Maximum AR Scale and Precipitation Maps

The dots on the maps below represent the AR scale observed and forecast at each grid point. GEFS plots update about every six hours and ECMWF plots update about every 12 hours.

For more information on this product click here to view an overview video.

Show Precipitation:  



Past 7 days (observed)

Future 7 days (forecast):  

AR Scale Plume Diagrams

The map on the left shows the AR scale forecasted over the next 7 days from the ensemble mean or control forecast at each dotted location. The largest dot represents the chosen location for the middle and right plots.

The plot on the right shows where each identified AR falls on the AR Scale matrix and how the AR scale is calculated, identified by letters at the top of each AR in the center diagram. Time periods where IVT >250 kg m-1 s-1 but the duration is less than 24 hours will be represented by gray shading in the center diagram and ◯’s for time periods in the analysis (ie observed) period and X’s for time periods in the forecast on the right plot.

The plume diagram (center) represents the integrated water vapor transport (IVT) and AR scale analysis (ie observed) and forecast.

  • The left side of each plot (red date labels) represents the observed (i.e. the 0-hour analysis of the control forecast) for the previous 7 days.
  • The right side of each plot (blue date labels) represents each of the individual ensemble models (thin gray lines), the unperturbed GFS or ECMWF control forecast (black line), the ensemble mean (green line), and plus or minus one standard deviation from the ensemble mean (red line (+), blue line (-), and gray shading).
  • Colored shading represents the AR scale observed or forecast for the given time, shaded according to scale, calculated using the control forecast or ensemble mean.
  • At the top of the diagram each identified AR is given a letter representation (used on the right plot) and the maximum IVT during the AR (kg m-1 s-1), the AR duration (hours), and time integrated IVT (107 kg m-1) during the AR are shown.
  • Note that if an AR is currently being observed at the given location (AR shading over the center line), the AR Scale is calculated using a combination of analysis and forecast data.

For more information on this product click here to view an overview video.

Transect Location:



AR Scale Calculated by:

All model data provided courtesy of NOAA/NCEP or ECMWF. All products are considered experimental.