Changes Coming to River Flood Warnings

Beginning on November 1st, NWS Central Illinois will implement polygon-based Flood Warnings and Flood Statements for river forecast points in our area of responsibility. In the past, these county-based warnings highlighted entire counties on the Watch/Warning/Advisory (WWA) map on the front page of our website. Soon, only the area along the river in proximity to the forecast point will be highlighted. Other than outlining a more defined area, this change will also allow additional hazards to be displayed on the WWA map in areas impacted by other weather hazards.
Important Note: These polygons are not meant to signify areas of inundation. They are simply a means to graphically represent select rivers where we provide flood forecast and warning services.

The format of the text products will remain unchanged with the exception of a series of latitude/longitude pairs at the end. These are the anchor points for the polygons. Each river forecast location has a set of static points that will be included in all river Flood Warnings and follow-up Flood Statements. Below is an example...

&&
 
LAT...LON 3878 8846 3871 8829 3960 8820 3860 8832
      3867 8838 3870 8846
 
$$
 
This change to river Flood Warning Polygons has been coordinated and implemented across all NWS offices that service portions of Illinois. This includes:
NWS Central Illinois:http://www.crh.noaa.gov/ilx/

 

 

 


Old county-based river flood warnings vs. New polygon-based warnings.

                                                                                                                    



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