National Weather Service United States Department of Commerce

NDFD Verification General Help Page

What is this website?

This site contains some basic verification results for selected weather elements (e.g., temperature, dew point, wind speed, etc.) from the National Digital Forecast Database (NDFD).

Contents: How to Use This Site, Definitions of Weather Elements, Definitions of Statistics

How to Use This Site

  1. You should see a webpage with two sections: a left section and a main section.

    The left section contains several categories of menu options from which the user can select. As prompted by the "Welcome" message on the right, first select a month. The projection menu appears for maps, but not plots, since each map is unique to a projection, while the plots contain all projections.

    The main section displays the data and statistical products (currently, maps and plots) as selected by the menus on the left.

  2. The left section contains menus you can use to select the verification product in which you are interested. You will need to first select a month from the top menu. Notice that as you make selections, the options available in the other menus can change.

    The next category is called Element. The weather elements for which verification is available are displayed.

    The next category is called Ref Time. Currently, results based on 00Z and 12Z NDFD forecasts are available.

    Next, select Product desired. Current options are plot, map, and text.
    Plot files are graphs of statistics for all available projections. Map files are thematic maps of the statistics. The text files contain the statistics in ASCII format, suitable for spreadsheet use The set of statistics, and thus maps/plots/files, will change according to the weather element.

    Lastly, for maps, which have individual results for projection,a Projection menu is provided.

    Please note:
    All statistics for a given selection are presented in the main section. If Dew Point Map is selected, then maps of the MAE and Bias are given.

  3. Point-based verification results are available for these weather elements:
    • Max Temp
    • Min Temp
    • PoP 12
    • Dew Point
    • Sfc Temp
    • Wind Speed
    • Wind Dir
    • Sky Cover
    • Wind Gust
    • Relative Humidity

    Please note that the statistics available are dependent on the weather element chosen. The statistics used, particular to a certain weather element, are MAE (mean absolute error), bias (forecast minus the observation), Heidke Skill Score, Fraction Correct, Brier Score, and Relative Frequency. These are defined in the Definitions section of this page.

    To print a particular image, right-click on the image, then choose Print from your browser's File menu.

Definitions of Weather Elements

Definitions of Statistics