Wireless Emergency Alert (WEA) messages will be broadcast to cell towers located in geographic areas where the alerts apply, which in turn will relay the messages to all cell phones within reach of their signals.
"At 2 p.m. today we open[ed] the pipes, so our warnings will flow through the system," said NWS spokeswoman Susan Buchanan. "Ultimately, though, it's the wireless carriers that are implementing it; it's happening on a rolling basis across the country."
Wireless carriers participate in the alert program voluntarily. Among national carriers, Sprint and Verizon are fully ready, but there are hundreds of smaller carriers that have not yet enabled the broadcasts, even though they might have agreed to do so. A list of participating carriers is available on FEMA.gov.
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Not all cell phones, particularly older models, are capable of receiving the alerts, Buchanan said. FEMA notes that some cell phone models might be upgradable, and all new cell phones on the market by the end of 2014 should have the capability. A list of models that are able to receive the alerts can be found on the website of CTIA, the wireless industry's trade association.
The severe weather texts will go out as quickly as possible. Mike Gerber, NWS' emerging dissemination technologies program lead, said tests were conducted in New York in December, looking in part at how quickly a WEA message would reach citizens. "They indicated it happened in a matter of seconds," he said.
The system does not use GPS. Gerber described it as "point to multi-point." The alerts are sent to cell towers, not to cell phones. This way, if you live in Virginia but happen to be in Florida when a hurricane hits, you will be notified of an impending storm. If you were home in Virginia, you would not receive the alert, appropriately. Another advantage to this approach is that it's not subject to congestion, Gerber said.
NWS uses the World Meteorological Organization format of messaging, which has to be converted to Common Alerting Protocol v1.2, which is used by FEMA's Integrated Public Alerts and Warning System (IPAWS) and its Commercial Mobile Alert System. The messages are limited to 90 characters, so they only convey urgent information.
WEAs are limited to warnings. They do not include severe weather watches, and they only address certain weather conditions: blizzards and ice storms, dust storms, extreme winds, flash floods, hurricanes and typhoons, tornadoes, and tsunamis.
"They only are intended to be a bell ringer," Gerber said. "They're not intended to replace other sources of information. They're simply, 'Here's the action you need to take, and get additional information from other sources," such as a weather radio.
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