National Weather Service United States Department of Commerce

Frequently Asked Questions

  1. What is the NDFD?
    Click here to learn more about the National Digital Forecast Database.

  2. What stations are used in NDFD verification? Which National Weather Service Forecast Office does each station belong to?
    See the following station list.

  3. What are the station lat/lon's and which grid cell lat/lon are they compared to?
    See the following point verification locations.

  4. How are the National Weather Service Forecast Offices split into regions?
    See the following National Weather Service Forecast Office locations.

  5. What exactly is the "00Z NDFD"? Similarly, what is the "12Z NDFD"?
    The 00Z NDFD is what could be called a "snapshot" of the NDFD at the 00Z reference time. In other words, the 00Z NDFD consists of the forecasts available at 00Z on the NDFD. Similarly, the 12Z NDFD consists of the forecasts available at 12Z on the NDFD.

    Note: The NDFD refers to the issuance time, or when the forecasts go out, as the "reference time". The "valid time", in NDFD terminology, is reserved for the time when the forecast comes true. In the case of a forecast for a time range, the valid time is the end of the time range. So 00Z NDFD is the set of forecasts which have a 00Z "reference" time.

  6. Do you quality control the data prior to computing scores?
    NDFD forecasts are not checked for quality. Since these are essentially the forecasts available to the public, we don't eliminate any values from the sample. NOTE: we assume a user of the publicly-available 2.5 km grids would use an interpolation or nearest-neighbor technique to obtain point forecasts similar to ours. For various reasons, the NDFD point forecasts may not match the PFM values. Some automated quality control of observations occurs to eliminate suspicious values. See the following link for a list of the gross error checks currently in use.

  7. How do you verify sky cover forecasts?
    Beginning in July 2007, we made major changes in the way we verify sky cover. See the following link for more information.

  8. Where can I find long-term NDFD verification?
    See our Publications page for long-term NDFD verification studies.

  9. Where can I find additional National Weather Service verification data?
    The verification projects with which MDL is involved are shown on our MDL Verification home page. Other verification data is available from the NWS Performance Management page. Questions about NWS forecast verification and data availability should be addressed to the Performance Branch at