NWS CAP v1.1 is being terminated. NWS CAP users should instead use CAP v1.2. Please see Service Change Notice (SCN) 17-35 for information about termination. See the NWS Common Alerting Protocol page for NWS sources of CAP v1.2 and updated documentation. An updated SCN will be released in the second half of 2022 with the projected termination date. Overview
This page provides guidance on the use of and access to NWS watches, warnings, advisories,
and other similar products in the Common Alerting Protocol (CAP) and Atom
Syndication Format (ATOM).
Information below refers to CAP v1.1.
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.
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 NWS CAP v1.1 Messages
-
CAP v1.1 was not intended to be used to activate EAS and should not be used for that purpose.
NWS CAP v1.1 format does not have all the data fields required to properly activate EAS and has
been known to cause errors and problems in the dissemination of NWS weather alerts and warnings.
-
It is assumed consumers of the CAP v1.1 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 v1.1 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 v1.1 messages;
-
NWS
provides shapefiles of NWS forecast zones that are provided in
the UGC system and also parsed into fields in the CAP v1.1 messages.
These are provided for all CAP v1.1 messages;
-
A list of possible data that is populated in the <event>
field is available here.
NWS CAP Support
-
To report real-time, operational CAP-related concerns, contact the NWS Telecommunications Center (TOC) at
301-713-0902 or email TOC.NWSTG@noaa.gov.
-
For CAP program or general information questions, email Mike.Gerber at noaa.gov
-
For technical CAP or production questions, email sdb.support at noaa.gov
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