Overview
This page provides access to NWS watches, warnings, advisories, and other similar products in the Common Alerting Protocol (CAP) and Atom Syndication Format (ATOM).
Use of ATOM and CAP with Traditional and Emerging Technologies
NWS CAP and ATOM feeds can be used to launch Internet messages, trigger alerting systems, feed mobile device (e.g., cell phone/smart phone and tablet) applications, news feeds, television text captions, highway sign messages, and synthesized voice over automated telephone calls or radio broadcasts.
CAP Overview
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 CAP messages are produced in the CAP v1.1 format defined by the Organization for the Advancement of Structured Information Standards (OASIS).
Developers and re-packagers of NWS CAP messages should review the Technical Notes about the NWS CAP 1.1 Messages.
NWS is now using a public access Wiki to act as a guide and collaborative venue for developers and re-distributors of NWS alerts in CAP.
ATOM Overview
ATOM is an XML based document format for syndicating news and other timely news-like information. The NWS ATOM feeds act as an index for active CAP messages by state, county, and NWS forecast zones to aid the automated dissemination of this information.
ATOM provides headlines, URLs to the source document and brief description information in an easy to understand and use format. Software libraries exist to read the ATOM format and present ATOM headlines on webpages, personal computer workstations, and mobile devices. For consumers of these feeds as indexes to the CAP messages, the ATOM feeds contain several CAP data fields to assist in the tracking of available CAP messages with the goal of reducing the need to query the complete CAP message at every refresh.
Navigating to the NWS CAP and ATOM Feeds
This page leverages the ATOM feed as an index to help you find active CAP messages for a given state, county, or NWS forecast zone. Developers and re-packagers of NWS alerts should note that each ATOM feed contains several CAP data fields to assist in the tracking of available CAP messages with the goal of reducing the need to query the complete CAP message at every refresh.
Select any state to see a list of alerts for that state (note: you may subscribe to one of the state ATOM feeds by selecting the ATOM logo  in the second column). Alternatively, you may select from the "By County/Zone" column to select from a list of counties or NWS forecast. In many locations, the forecast zones roughly follow county lines.
The resulting page is the ATOM feed reformatted for your web browser using a custom Extensible Stylesheet Language (XSL) style sheet and lists all active CAP messages (i.e., alerts) for the respective area. XSL describes how files encoded in the XML standard are to be formatted or transformed for display by your web browser. The actual ATOM Feed can be viewed by viewing the page source (e.g., right click on browser and click View Page Source).
To view the details of an alert, select the name or issued/expiring time of the alert. The resulting page is the CAP message of the alert reformatted for your web browser using a second custom XSL style sheet. The actual CAP message can be viewed by viewing the page source.
The ATOM and CAP feeds are updated about every two minutes.
More information on NWS CAP and ATOM feeds is available in the Service Description Document for NWS Watches, Warnings, and Advisories using CAP and ATOM based Formats.
Technical Notes about the CAP 1.1 Messages
- It is assumed consumers of the CAP 1.1 feeds will use the ATOM index files to track active alerts in near real time and pulling the complete CAP messages as needed;
- The ATOM indexes contain a number of CAP 1.1 fields as an extension to the ATOM fields (thus the switch from RSS to ATOM in this version). These fields are included to provide additional information to the consumer with the intent of reducing the need to pull the entire CAP message every time;
- An XML style sheet is used to display the CAP message in a human readable format in modern web browsers. Not all CAP fields are displayed in the human view. Be sure to view the message source to see all available fields;
- NWS based UGC and VTEC codes have been parsed out to provide cross reference to these code systems.
- SAME codes are provided when available (not all NWS products are issued with a SAME code);
- NWS Storm Based Warning lat/lon pairs are made available when provided. Not all NWS products are issued with this information;
- County FIPS codes are provided for all CAP 1.1 messages;
- NWS provides shapefiles of NWS forecast zones that are provided in the UGC system and also parsed into fields in the CAP 1.1 messages. These are provided for all CAP 1.1 messages;
- A list of possible data that is populated in the <event> field is available here.
- NWS is now using a public access Wiki to act as a guide and collaborative venue for developers and re-distributors of NWS alerts in CAP.
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