The National Weather Service is expanding a pilot program last year that will change how you get weather warnings.
The Impact Based Warning approach seeks to provide more information about what kind of damage people could expect from severe storms. Take tornadoes, for example. The warnings seek to distinguish between radar indicated tornadoes, those which radar says exist but are otherwise unconfirmed, and those which are observed by spotters, law enforcement, or other sources.
There are two damage "tags" that can be used. Most tornadoes won't need one, according to the NWS, because most tornadoes are weak and short lived.
Tags begin "Tornado Damage Threat" and end with either "considerable" or "catastrophic." The former is used when evidence suggests a tornado will be long lived, capable of producing considerable damage and, "is imminent or ongoing."
Instructions with the catastrophic tag indicate it should be used "exceedingly rarely," and only when a violent tornado is observed and confirmed. How rare and how violent? The example the NWS uses for it was the Joplin tornado.
The initial pilot program involved Kansas and Missouri in 2012. This year's expansion covers those states plus 12 more. You can read about the program by clicking here.