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National Digital Forecast Database XML Web Service Use Guidelines

Access to the services is through an infrastructure with limited resources. As the popularity of the service has grown, NWS has added capacity as resources allow. A challenge of offering these services is also a strength: the creativity of our customers to use these services in ways never imagined. This creativity can also strain our resources at times. Below are some guidelines of use for the NDFD XML Web Service located at

  • It is recommended a client not make more than one request every five seconds.
  • The forecast data is updated no more than twice an hour (at approximately 25 and 55 minutes after the hour). Do not request data for the same location more than twice an hour.
  • Shorten the time window for data to be returned, if all days (7 for most elements) are not needed. This means adjusting the startTime/begin and endTime/end query parameters values in a time-series or glance request, or adjusting the startDate and numDays query parameters in the 12 or 24 hourly summarization products.
  • Please do not set the startTime/begin, endTime/end query parameters to your system clock time with seconds in the time. Please set these times to resolutions no less than hourly (i.e. 2022-10-02T09:00:00, and not 2019-10-02T09:17:22)
  • Please request data for only elements (temperature, max temperature, wind speed, probability of hail, etc) that you need.
  • Due to the increase in both temporal and spatial resolution of NDFD data from 3 hourly and 5 kilometer, to hourly and 2.5 kilometer, respectively, a query with more than 100 lat/long points is not allowed (on the lower resolution version of the NDFD XML Web Service on graphical, 200 pts was allowed). Depending on resource, this 100 point allowance may change. Also, if you are requesting many many meteorological elements in a single time-series query, or are requesting a product with a lot of data (the 12 or 24 hourly summary products, a cities request, etc) please make an attempt to request these data with less lat/lon points, and/or less elements. It's better to break up a resource intensive query into more smaller queries with less points and/or elements. Please "find" or "experiment" with breaking very large queries into more smaller queries to suit your needs. For example, break up a 100-point query into four 25-point queries. Or break up a query with 40 elements into two queries with 20 elements, etc.
  • Please designate latitude and longitude query parameter values to no more than 2 decimal places (i.e. 38.76, -77.32).
  • NOTE: The Akamai Server caches and buffers requests if they are exactly the same queries.
       Page last Modified: 18 Apr, 2022 10:31 AM