IEM Cow (NWS Storm Based Warning Verification)
Data presented here is unofficial and should be used for educational purposes only. This application allows you to view warnings and storm reports issued by a Weather Forecast Office (WFO) for a period of time of your choice. The application attempts to automatically provide verification numbers for the warnings issued.
This application works for dates after 8 June 2005.
Storm Based Warnings
On the first of October 2007, the National Weather Service began issuing warnings for tornados, severe weather, floods, and marine hazards on a storm by storm basis. Previously, the warnings were issued for an entire county. This application attempts to provide verification statistics for these storm based warnings.
The images shown are taken from the NWS Storm Based Warnings website.
The map on the left illustrates some of the spatial statistics the Cow produces. The following is a brief description of these values.
- SBW Area: (P) (black/white outline polygon) This is the areal size of the polygon expressed in square kilometers. The computation is done in the projection "US National Atlas Equal Area" (EPSG 2163).
- County Area: (C) (red outline polygon) Each storm based warning is associated with one or more counties. This value is the total area of the associated counties. Same projected used as above.
- Size % (C-P)/C This is the size reduction percentage of the storm based warning versus the counties. Prior to SBW, the warning would have included the entire area of the county. So larger reduction values are desired.
- Perimeter Ratio: (purple line) This is an attempt to determine how much of the storm based warning perimeter is being influenced by a county political boundary. The ratio is simply the portion of the SBW perimeter that closely coincides with a political boundary. A 100% value implies the warning is simply a retracement of county borders.
- Verification Area %: (filled ovals) Local Storm Reports are buffered out in a circular fashion and combined to create a coverage of impacted areas. The area of the buffered LSRs is then compared with the area of the storm based warning to yield a percentage.