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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 except for the Transition
from CAP v1.1 to v1.2 section immediately below and the Technical
Notes about the NWS CAP v1.2 Messages and Methods to get NWS CAP
v1.2 Messages sections near the bottom of the page.
Transition from CAP v1.1 to v1.2
NWS CAP v1.2 will be available from more sources, will simplify
alert tracking, and have improved documentation. The NWS is far
along in a yearlong process to transition CAP messages from CAP v1.1
to v1.2. Watch this page for updates as progress is made and
timelines announced. During the transition, there will be an overlap
period of 60 days or more when both CAP v1.1 and CAP v1.2 will be
supported with CAP messages and associated Atom index feeds.
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
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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.
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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;
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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;
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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;
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NWS based UGC
and VTEC codes have
been parsed out to provide cross reference to these code systems.
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SAME codes
are provided when available (not all NWS products are issued with a
SAME code);
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NWS Storm Based
Warning lat/lon pairs are made available when provided. Not all
NWS products are issued with this information;
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County
FIPS codes are provided for all CAP v1.1 messages;
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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;
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A list of possible data that is populated in the <event>
field is available here.
Technical Notes about the NWS CAP v1.2 Messages
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All of the Technical Notes about CAP v1.1 messages in the section above also pertain to CAP v1.2 messages.
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New for NWS CAP v1.2 are CAP "push" services described below. CAP v1.2 and updated Atom feed will also be
available for "pull" before the end of 2013 at http://alerts.weather.gov. There will be a minimum period of 60 days
overlap when both NWS CAP v1.1 and v1.2 will be available. Additional pull and push methods from the NWS are expected
during the last half of 2013. For the most reliable and resilient CAP service, obtaining NWS CAP alert messages
from multiple sources is recommended.
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NWS CAP v1.2 alerts are considered experimental at this time but have proven very reliable.
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The online National Weather Service CAP v1.2 Documentation
supplements the OASIS CAP v1.2 standard and
CAP v1.2 USA Integrated Public Alert and Warning System (IPAWS) Profile
Version 1.0 by identifying the formats of NWS information contained within NWS CAP v1.2 messages. A couple of new NWS
parameters are expected before NWS CAP v1.2 becomes operational.
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CAP v1.2 messages on NWS web pages and received via NWS push methods MUST NOT be used as input into EAS encoder/decoder
boxes to activate EAS until an announcement that NWS CAP is suitable for EAS service. Activation of EAS for NWS watches
and warnings should only be done based on NOAA Weather Radio (NWR) Specific Area Message Encoding audio feed and on
standard NWS text messages.
Methods to get NWS CAP v1.2 Messages
***PULL***
The major advantage of the Atom feeds and the pull is that it is easy and inexpensive to implement with little or no resources.
The disadvantage is the inherent delay introduced by a pull service like alerts.weather.gov. The NWS CAP v1.2 pull has 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 (ex. Tornado Warnings) are extremely time sensitive.
NWS CAP v1.2 alerts will soon be available via the following pull methods:
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FEMA IPAWS will be a good source to pull NWS CAP v1.2 alerts because both weather and non-weather alert messages will
be available from that single source. FEMA IPAWS requires application for access with FEMA. For more information,
view the FEMA web page at http://www.fema.gov/internet-service-providers.
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Software developers are encouraged to participate in regular FEMA IPAWS Practitioner and Developer webinars to learn
how to get and use CAP alerts from IPAWS. To sign up for future webinar notices and to view many of the past recorded
webinars, click through https://www.fema.gov/integrated-public-alert-and-warning-system-working-groups.
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Additional pull methods coming soon.
***PUSH***
The major advantage of most push methods is timeliness. The results of the several months of experimental NWS CAP v1.2
push via NOAAPORT and NWWS shows CAP availability typically less than 45 seconds from creation with very high reliability.
A frequently expressed disadvantage is a higher cost due to equipment and software resource needs.
NWS push methods use discrete message or product identifiers called World Meteorological Organization (WMO) headings and Advanced Weather Interactive Processing System (AWIPS)
identifiers. A listing of WMO headings and AWIPS identifiers for NWS CAP v1.2 messages is available here.
Note the six (6) XOaaii CCCC CAPxxx identifiers for the national centers at the end of the listing are included as
placeholders for future use. CAP v1.2 national center messages are not now being created for pull or push methods.
NWS CAP v1.2 alerts are currently via the following push methods:
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NOAAPORT - NOAAPORT is the most robust mechanism for receiving NWS CAP v1.2 messages. The initial cost for NOAAPORT
is highest among NWS CAP push services. For more information about NOAAPORT, please see
http://www.nws.noaa.gov/os/disemsys.shtml.
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NWWS is the second most robust mechanism for receiving NWS CAP v1.2 messages.
NWWS is available as a satellite-based and Internet-based service.
For more information about NWWS, please see http://www.nws.noaa.gov/os/disemsys.shtml.
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Additional push methods coming soon.
NWS CAP Support
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To report real-time, operational CAP-related concerns, contact the NWS Telecommunications Center (TOC) at
301-713-0902 or email TOC.NWSTG@noaa.gov.
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For CAP program or general information questions, email Mike.Gerber at noaa.gov
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For technical CAP or production questions, email Robert.Bunge at noaa.gov
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