Storm Based Warning Initiative
The National Weather Service at Indianapolis is now issuing storm based warnings versus warnings by entire county. This is accomplished by drawing a polygon in the expected path of the severe storm. The polygon represents an area where the maximum threat for severe weather exists and is defined by a shape with at least four sides.
Prior to 2005, the NWS issued severe weather warnings based on counties. For example, if a severe thunderstorm was going to move across southeast Marion county, the entire county was placed in a severe thunderstorm warning. Under the polygon method, only the southeast section of the county would be in a warning.
Issuing storm based warnings offers several advantages. The graphic version of the warning allows you to clearly see the specific area that is under the threat for severe weather. Also, fewer people are needlessly warned for severe weather that will not affect their location.
How do storm based warnings work?
The polygons for storm based warnings are drawn by NWS Meteorologists based on where the greatest threat for severe weather is. The warning software then generates the text of the warning based on the polygon. Counties affected by the warning are listed. The corners of the polygon are defined by a set of latitude and longitude points, and these points are displayed at the bottom of the text of the warning.
Below is an example of an actual storm based warning (polygon) issued in 2006:
The storm based warning is for parts of Greene, Owen, and Monroe counties of central Indiana (county borders are highlighted in yellow). The white shape in the picture is the warning polygon. Portions of the actual text of the warning are below:
THE NATIONAL WEATHER SERVICE IN INDIANAPOLIS HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR...
WESTERN MONROE COUNTY IN SOUTH CENTRAL INDIANA
THIS INCLUDES THE CITY OF BLOOMINGTON
NORTHEASTERN GREENE COUNTY IN SOUTHWEST INDIANA
SOUTHEASTERN OWEN COUNTY IN WEST CENTRAL INDIANA
* UNTIL 400 PM EDT
* AT 320 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL. THIS
STORM WAS LOCATED NEAR WORTHINGTON...OR ABOUT 25 MILES WEST OF
BLOOMINGTON...AND MOVING EAST AT 30 MPH.
* THE SEVERE THUNDERSTORM WILL BE NEAR...
ELLETTSVILLE AROUND 355 PM EDT...
BLOOMINGTON AROUND 400 PM EDT...
LAT...LON 3915 8710 3898 8704 3908 8647 3931 8658
The LAT…LON line at the bottom of the warning are the latitude and longitude coordinates of the four corners of the polygon.
Where Can I View the Storm Based Warnings?
The NWS Indianapolis homepage has links to the current radar, and the storm based warning polygons can be displayed on the radar image. The NWS also provides the ability to view radar and polygon on wireless devices such as PDAs and cell phones. Polygons are also available on third party websites, such as commercial or university websites.
Are There Other Uses for the Storm Based Warning Polygons?
Some businesses offer a service where you can be called if your location falls within a polygon. The media can also show the polygons to convey the threat area for the storm.
Can a County Be Under Two Warnings at the Same Time?
Yes, and an example of a county under two warnings at the same time can be seen below. Fountain county has two severe thunderstorm warnings in effect. One warning is for the northern part of the county, while another warning is in effect across the southern part of the county for a different storm. Each storm has its own severe weather threat.
Will SAME encoding work as before?
Yes. Any county within a warning polyon will still be coded the same as they were before. No changes need to be made to weather radios.
How Can I Provide Feedback on the Warnings or Ask Questions?
You can contact the National Weather Service via email at w-ind.webmaster@noaa.gov , or you can call us at 317-856-0360.
Where Can I Find More Information on Storm Based Warnings?
http://www.weather.gov/sbwarnings/
