Polygon Warning Statistics For 2004 & 2005 Polygon Warning Team Meeting Fort Worth TX Ken Waters NWS Regional Scientist National Weather Service Pacific Region Headquarters Honolulu, Hawaii October 25, 2005

Outline The Process The Process Quality Control Issues Quality Control Issues Overview of warnings for 2004 & 2005 Overview of warnings for 2004 & 2005 Results for WFOs participating in the test vs. nonparticipating WFOs Results for WFOs participating in the test vs. nonparticipating WFOs

The Process Collect the warnings from OCWWS’ FTP server Collect the warnings from OCWWS’ FTP server Scan all warnings, parsing relevant information (VTEC, polygon, etc.) and write to a single warning file Scan all warnings, parsing relevant information (VTEC, polygon, etc.) and write to a single warning file Quality control the data Quality control the data Create shapefiles for TOR, SVR, FFW, and SMW from the data Create shapefiles for TOR, SVR, FFW, and SMW from the data Quality control the data more based on visual inspection of the GIS graphics Quality control the data more based on visual inspection of the GIS graphics Repair “ring order” geometry (Warngen is not consistent in the ordering of the vertices; GIS software requires clockwise ordering) Repair “ring order” geometry (Warngen is not consistent in the ordering of the vertices; GIS software requires clockwise ordering)

The Process Set the datum to North American NAD 83 and project into the Albers Equal Area projection for North America Set the datum to North American NAD 83 and project into the Albers Equal Area projection for North America Calculate the area (PWA) for each polygon warning and repopulate it back into the data attributes for the shapefile Calculate the area (PWA) for each polygon warning and repopulate it back into the data attributes for the shapefile Write out the shapefile as a “CSV” (comma separated variables) file Write out the shapefile as a “CSV” (comma separated variables) file Intersect each shapefile with the counties shapefile to determine the CEA (county equivalent area) values Intersect each shapefile with the counties shapefile to determine the CEA (county equivalent area) values Import results into Excel to organize and compute the CAR (county area ratios) Import results into Excel to organize and compute the CAR (county area ratios)

Quality Control Issues Data quality issues Data quality issues –Warnings with no polygons Much less common in 2005 than 2004 Much less common in 2005 than 2004 Have to completely remove the record since there is no value without a polygon Have to completely remove the record since there is no value without a polygon

Quality Control Issues Warnings with “one-point” polygons Warnings with “one-point” polygons –Presumed bug in Warngen –Identified to OCWWS and FSL to correct –Again, have to remove the record as there’s no useful polygon

Quality Control Issues Last digit of longitudes missing Last digit of longitudes missing Have to add a zero to longitude to prevent it from going back to the Prime Meridian Have to add a zero to longitude to prevent it from going back to the Prime Meridian Comms error? Comms error? Happens several times each year Happens several times each year

The Numbers (after the unusable warnings are removed) TORSVRFFWSMWTotal 20043,61120,1004,7592,633*31, (Jan-Sep) 2,53419,8962,9352,265*27,630 Total6,14539,9967,6944,898*58,733 *SMWs were archived but not used for CAR statistics due to their marine extent

2004 Warnings

2005 Warnings

Ground Zero in 2005 Tornado Outbreak + Hurricanes

Methodology Compute area of each polygon warning (PWA=Polygon Warning Area) Compute area of each polygon warning (PWA=Polygon Warning Area) Sum up area of all counties identified by their UGCs in the warning (CAE=County Area Equivalent) Sum up area of all counties identified by their UGCs in the warning (CAE=County Area Equivalent) Compute CAR (County Area Ratio): Compute CAR (County Area Ratio):

Nashville WFO Actual tornado warning 6/14/2005

Data Issues Affecting CARs Polygons stretching from one CWA to adjacent CWA Polygons stretching from one CWA to adjacent CWA –Reduces CAE due to not counting counties in adjacent CWA; increases CAR Overextending pathcast Overextending pathcast –Increases PWA, thus increases CAR

The Big and the Small - TOR

The Big and the Small - SVR

The Big and the Small - FFW

Average Size of Warnings -- Nationwide Sq Mi. (# Warnings) TOR (3,611) (2,534) SVR (20,100) (19,896) FFW (4,759) (2,935)

The Final Results (Jan-Sep) Change CAR % % False Alarm Improvement (100%-CAR) % % % (Jan-Sep)Change % % % % % TESTNON-TEST

Conclusions Average size of warnings increased slightly (why?) Average size of warnings increased slightly (why?) Areal percentage of counties decreased overall Areal percentage of counties decreased overall Areal percentage of counties decreased most notably for Polygon Warning test sites Areal percentage of counties decreased most notably for Polygon Warning test sites Several significant quality control issues dealing with Warngen and policy that should be addressed Several significant quality control issues dealing with Warngen and policy that should be addressed