Atmospheric River Scale Forecast Products

Ensemble Forecast Systems

Coastal Maximum AR Scale and Quantitative Precipitation Maps

The dots on the maps below represent the AR scale analysis and forecast from the Global Ensemble Forecast System (GEFS) or European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) at each grid point. The left map represents the AR scale observed over the previous 7 days from the 0-hour analysis of the GFS or ECMWF control forecast as well as the 7-day quantitative precipitation estimate from NCEP Stage-IV. The right map represents the AR scale forecasted over the next 7 days from the ensemble mean or control forecast of the GEFS or ECMWF and 7-day quantitative precipitation estimate. The AR scale is determined based on the duration of AR conditions and maximum IVT during the AR as described in Ralph et al. 2019 . Use the menus to select if the GEFS or EPS is displayed, if the control forecast or ensemble mean is used to calculate the AR Scale, and for coastal or inland locations. Use the button below to turn precipitation fields on and off.

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AR Scale Plume Diagrams

The plume diagrams below represent the integrated water vapor transport (IVT) and AR scale analysis and forecast from the GEFS or ECMWF EPS. The left side of each plot represents the 0-hour analysis of the control forecast for the previous 7 days. The right side of each plot 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 each AR 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. The plot on the left shows where each identified AR falls on the AR Scale matrix and how the AR scale is calculated, represents an AR in the analysis period and X represents a forecasted AR.

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AR Scale Ensemble Diagnostics

Top left: The plume diagram represents the integrated water vapor transport (IVT) forecast for 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 forecast for the given time, shaded according to scale, calculated using the model control forecast. Bottom left: Shading represents the probability of AR Scale conditions at the given location calculated by the number of ensemble members predicting a given AR Scale at each forecast lead time. Top right: Dots on the map represent the maximum AR Scale forecast from the GFS or ECMWF control member at that grid point for the next seven days. Colored shading represents the GFS or ECMWF 7-day accumulated precipitation forecast. The enlarged dot indicates the location the other plots in this diagram are representative of. Bottom right: AR Scale magnitude and timing calculated for each GEFS or ECMWF EPS ensemble members shaded according to scale. Values in shading represent the magnitude and timing of maximum IVT during each forecasted AR. Gray shading in each panel represents IVT >250 (kg m-1s-1 for a duration less than 24 hours.

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NCEP Global Forecast System (GFS)

AR Scale Forecast Maps

Plot Description: Forecasted AR scale based on the 0.25° hourly Global Forecast System (GFS) model, integrated vapor transport (IVT, kg m-1 s-1, and duration of AR conditions. The AR scale at each timestep represents the extent of a given AR at that time calculated based on the full 5 day forecast of that AR. The maximum AR Scale (bottom right of four panel plot) displays the maximum AR Scale at each grid point during the five day forecast.

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