Polygon Warning Statistics Polygon Warning Statistics For 2004 & 2005For 2004 & 2005

Polygon Warning Team MeetingPolygon Warning Team MeetingFort Worth TXFort Worth TX

Ken WatersKen WatersNWS Regional ScientistNWS Regional Scientist

National Weather ServiceNational Weather ServicePacific Region HeadquartersPacific Region Headquarters

Honolulu, HawaiiHonolulu, Hawaii

October 25, 2005October 25, 2005

OutlineOutline

• The ProcessThe Process

• Quality Control IssuesQuality Control Issues

• Overview of warnings for 2004 & Overview of warnings for 2004 & 20052005

• Results for WFOs participating in the Results for WFOs participating in the test vs. nonparticipating WFOstest vs. nonparticipating WFOs

The ProcessThe Process• Collect the warnings from OCWWS’ FTP serverCollect the warnings from OCWWS’ FTP server• Scan all warnings, parsing relevant information Scan all warnings, parsing relevant information

(VTEC, polygon, etc.) and write to a single (VTEC, polygon, etc.) and write to a single warning filewarning file

• Quality control the dataQuality control the data• Create shapefiles for TOR, SVR, FFW, and SMW Create shapefiles for TOR, SVR, FFW, and SMW

from the datafrom the data• Quality control the data more based on visual Quality control the data more based on visual

inspection of the GIS graphicsinspection of the GIS graphics• Repair “ring order” geometry (Warngen is not Repair “ring order” geometry (Warngen is not

consistent in the ordering of the vertices; GIS consistent in the ordering of the vertices; GIS software requires clockwise ordering)software requires clockwise ordering)

The ProcessThe Process

• Set the datum to North American NAD 83 and project Set the datum to North American NAD 83 and project into the Albers Equal Area projection for North into the Albers Equal Area projection for North AmericaAmerica

• Calculate the area (PWA) for each polygon warning Calculate the area (PWA) for each polygon warning and repopulate it back into the data attributes for the and repopulate it back into the data attributes for the shapefileshapefile

• Write out the shapefile as a “CSV” (comma separated Write out the shapefile as a “CSV” (comma separated variables) filevariables) file

• Intersect each shapefile with the counties shapefile Intersect each shapefile with the counties shapefile to determine the CEA (county equivalent area) valuesto determine the CEA (county equivalent area) values

• Import results into Excel to organize and compute the Import results into Excel to organize and compute the CAR (county area ratios)CAR (county area ratios)

Quality Control IssuesQuality Control Issues

• Data quality issuesData quality issues– Warnings with no Warnings with no

polygonspolygons•Much less common Much less common

in 2005 than 2004in 2005 than 2004•Have to completely Have to completely

remove the record remove the record since there is no since there is no value without a value without a polygonpolygon

Quality Control IssuesQuality Control Issues

• Warnings with Warnings with “one-point” “one-point” polygonspolygons– Presumed bug in Presumed bug in

WarngenWarngen– Identified to Identified to

OCWWS and FSL OCWWS and FSL to correctto correct

– Again, have to Again, have to remove the remove the record as record as there’s no useful there’s no useful polygonpolygon

Quality Control IssuesQuality Control Issues• Last digit of Last digit of

longitudes longitudes missingmissing

• Have to add a Have to add a zero to longitude zero to longitude to prevent it from to prevent it from going back to the going back to the Prime MeridianPrime Meridian

• Comms error?Comms error?• Happens several Happens several

times each yeartimes each year

The NumbersThe Numbers(after the unusable warnings are removed)(after the unusable warnings are removed)

TORTOR SVRSVR FFWFFW SMWSMW TotalTotal

20042004 3,6113,611 20,1020,1000

4,7594,759 2,6332,633**

31,1031,1033

2005 2005 (Jan-Sep)(Jan-Sep)

2,5342,534 19,8919,8966

2,9352,935 2,2652,265**

27,6327,6300

TotalTotal 6,1456,145 39,9939,9966

7,6947,694 4,8984,898**

58,7358,7333

*SMWs were archived but not used for CAR statistics due to their marine extent

2004 Warnings2004 Warnings

2005 Warnings2005 Warnings

Ground Zero in 2005Ground Zero in 2005Tornado Outbreak + HurricanesTornado Outbreak + Hurricanes

MethodologyMethodology

• Compute area of each polygon Compute area of each polygon warning (PWA=Polygon Warning warning (PWA=Polygon Warning Area)Area)

• Sum up area of all counties Sum up area of all counties identified by their UGCs in the identified by their UGCs in the warning (CAE=County Area warning (CAE=County Area Equivalent)Equivalent)

• Compute CAR (County Area Ratio):Compute CAR (County Area Ratio):

CAE

PWACAR

Nashville WFONashville WFOActual tornado warning 6/14/2005Actual tornado warning 6/14/2005

Data Issues Affecting CARsData Issues Affecting CARs• Polygons stretching from Polygons stretching from

one CWA to adjacent CWAone CWA to adjacent CWA– Reduces CAE due to not Reduces CAE due to not

counting counties in counting counties in adjacent CWA; increases adjacent CWA; increases CARCAR

• Overextending pathcastOverextending pathcast– Increases PWA, thus Increases PWA, thus

increases CARincreases CAR

CAE

PWACAR

The Big and the Small - TORThe Big and the Small - TOR

The Big and the Small - SVRThe Big and the Small - SVR

The Big and the Small - FFWThe Big and the Small - FFW

Average Size of WarningsAverage Size of Warnings-- Nationwide-- Nationwide

Sq Mi. (# Warnings)Sq Mi. (# Warnings)

20042004 20052005

TORTOR 352.1 (3,611)352.1 (3,611) 397.2 (2,534)397.2 (2,534)

SVRSVR 491.4 491.4 (20,100)(20,100)

499.3 499.3 (19,896)(19,896)

FFWFFW 909.9 (4,759)909.9 (4,759) 912.4 (2,935)912.4 (2,935)

The Final ResultsThe Final Results

20042004 2005 2005 (Jan-Sep)(Jan-Sep)

ChangeChange

CARCAR 35.48 %35.48 % 27.93 %27.93 %

False Alarm False Alarm ImprovemenImprovement (100%-t (100%-CAR)CAR)

64.52 %64.52 % 72.07 %72.07 % + + 11.07%11.07%

20042004 20052005(Jan-Sep)(Jan-Sep)

ChangeChange

36.37 %36.37 % 30.86 %30.86 %

63.63 %63.63 % 69.24 %69.24 % + 8.82 %+ 8.82 %

TEST

NON-TEST

ConclusionsConclusions

• Average size of warnings increased slightly Average size of warnings increased slightly (why?)(why?)

• Areal percentage of counties decreased overallAreal percentage of counties decreased overall

• Areal percentage of counties decreased most Areal percentage of counties decreased most notably for Polygon Warning test sitesnotably for Polygon Warning test sites

• Several significant quality control issues dealing Several significant quality control issues dealing with Warngen and policy that should be with Warngen and policy that should be addressedaddressed