What is CAP?

Common Alerting Protocol (CAP)  is an XML-based information standard used to facilitate emergency information sharing and data exchange across local, state, tribal, national and non-governmental organizations of different professions that provide emergency response and management services.

NWS produces CAP for NWS weather and hydrologic alerts including watches, warnings, advisories, and special statements. 

NWS CAP messages follow the CAP v1.2 standard defined by the Organization for the Advancement of Structured Information Standards (OASIS) and comply with the Federal Emergency Management Agency (FEMA) Integrated Public Alert and Warning System (IPAWS) CAP profile.  The National Weather Service (NWS) CAP v1.2 Documentation provided on this site supplements the OASIS CAP v1.2 standard and IPAWS CAP profile by identifying the formats of NWS information contained within NWS CAP messages. 

Uses of CAP

NWS CAP can be used to launch Internet messages, trigger alerting systems, feed mobile device applications, news feeds, television/radio display and audio, digital highway signs, synthesized voice over automated telephone calls, and much more.

How to Get NWS CAP Messages

NWS CAP messages are available through multiple dissemination channels.

Pull

CAP consumers should note there is an inherent delay introduced by pull services. NWS CAP pull capabilities have been designed and engineered to reduce the delay as much as possible. It should be understood that it is only as fast as the client is configured to pull it - every 2, 5, 10, even 15 minutes - based on the consumer’s own technical needs and constraints. It should be understood that some alerts (e.g. Tornado Warnings) are extremely time sensitive.

  1. NWS recommends use of the NWS Application Programming Interface (API) for access to NWS CAP messages.  The API also provides a digest of active NWS CAP messages in ATOM format and CAP content in JavaScript Object Notation (JSON) format. 

  2. A secondary method for pulling NWS CAP messages is via the http and ftp file listings at http://tgftp.nws.noaa.gov/SL.us008001/DF.xml/DC.cap/ and  ftp://tgftp.nws.noaa.gov/SL.us008001/DF.xml/DC.cap/  These file listings provide a traditional directory listing of all  CAP messages issued for the past 7 days as well as directory lists (ls-l and ls-lt) for CAP consumers wishing to check for any new CAP messages in the directory.  The http and ftp file listings are not recommended as a primary source for NWS CAP messages.

Push

NWS CAP v1.2 alerts are currently via the following push methods:

  1. NOAAPORT is the most robust mechanism for receiving NWS CAP messages. The initial cost for NOAAPORT is highest among NWS CAP push services.

  2. NOAA Weather Wire Service (NWWS) is the second most robust mechanism for receiving NWS CAP v1.2 messages. CAP is available over NWWS as a satellite-based service and over the NWWS Internet-based service known as NWWS Open Interface (OI). 

The major advantage of most push methods is timeliness. NWS CAP messages pushed via NOAAPORT and NWWS are typically available less than 45 seconds from creation with very high reliability. A disadvantage of push can be higher cost due to equipment and software requirements.

NWS push methods use discrete message or product identifiers called World Meteorological Organization (WMO) headings and Advanced Weather Interactive Processing System (AWIPS) identifiers. See the listing of WMO headings and AWIPS identifiers for NWS CAP v1.2 messages.