Probabilistic Forecasting Software Application Information

Generating Probabilistic Grids

Once you have defined deterministic grids and have set the models weights to values you think appropriate, you can then generate two additional grids that represent uncertainty in your forecast, the 10th percentile and the 90th percentile grids. A GFE procedure assesses the uncertainty in the ensemble model suite and applies that to your deterministic forecast and generates the 10 and 90 grids. This section describes how to use the GenerateProbGrids tool.

GenerateProbGrids Tool

To create grids that express the uncertainty of your forecast, run the GenerateProbGrids tool.

Tool Set up

Before actually running the tool, perform the following set up steps.

  • Load the following weather elements into your GFE. These elements will be populated by grids generated by the tool:
    • T10Pct
    • T90Pct
    • Wind10Pct
    • Wind90Pct
  • Select the time range over which you want to run the tool in the Grid Manager.

Run the Tool

To run the tool, select the time range over which you want to generate your grids. Then select from the ProbTools menu: GenerateProbGrids. The tool will display a dialog that look like this.


Select the weather element for which you want to generate your grids followed by “Run/Dismiss”. As the tool executes, your deterministic grid, the entire set ensemble grids, and the weights for each model member are read. A histogram at each point is calculated and the 10 and 90 percentile values are calculated at each point. These values along with the weights and your deterministic grid (used as the 50 percentile grid) are combined to generate the 10 and 90 percentile grids for your forecast. Your 10 and 90 percentile grids will appear as they are calculated. If you selected a log time range (over 24 hours) it may take a minute of two to calculate all of your uncertainty grids.

Note: generating probabilistic grids for QPF has been disabled until we develop a better algorithm for generating these grids. QPF grids tend to be filled with many zeros, or many small values, rendering the resulting 10 and 90 percentile grids not very useful. As new techniques are developed we will update these tools.

Once your done generating your probabilistic grids, make sure that you save them in the GFE gridded database.