# Presentation: 738726

## 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
- Quality Control Issues
- Overview of warnings for 2004 & 2005
- Results for WFOs participating in the test vs. nonparticipating WFOs

## The Process

- Collect the warnings from OCWWS’ FTP server
- Scan all warnings, parsing relevant information (VTEC, polygon, etc.) and write to a single warning file
- Quality control 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
- 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
- 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
- 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)

## Quality Control Issues

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

## Quality Control Issues

- 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
- Have to add a zero to longitude to prevent it from going back to the Prime Meridian
- Comms error?
- Happens several times each year

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

|  | TOR | SVR | FFW | SMW | Total |
| --- | --- | --- | --- | --- | --- |
| 2004 | 3,611 | 20,100 | 4,759 | 2,633* | 31,103 |
| 2005 (Jan-Sep) | 2,534 | 19,896 | 2,935 | 2,265* | 27,630 |
| Total | 6,145 | 39,996 | 7,694 | 4,898* | 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)
- Sum up area of all counties identified by their UGCs in the warning (CAE=County Area Equivalent)
- Compute CAR (County Area Ratio):

## Nashville WFOActual tornado warning 6/14/2005

- Nashville WFOActual tornado warning 6/14/2005

## Data Issues Affecting CARs

- Polygons stretching from one CWA to adjacent CWA
- Reduces CAE due to not counting counties in adjacent CWA; increases CAR
- Overextending pathcast
- Increases PWA, thus increases CAR

## Slide 15

## Slide 16

## 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)

|  | 2004 | 2005 |
| --- | --- | --- |
| TOR | 352.1 (3,611) | 397.2 (2,534) |
| SVR | 491.4 (20,100) | 499.3 (19,896) |
| FFW | 909.9 (4,759) | 912.4 (2,935) |

## The Final Results

|  | 2004 | 2005 (Jan-Sep) | Change |
| --- | --- | --- | --- |
| CAR | 35.48 % | 27.93 % |  |
| False Alarm Improvement (100%-CAR) | 64.52 % | 72.07 % | + 11.07% |

| 2004 | 2005
(Jan-Sep) | Change |
| --- | --- | --- |
| 36.37 % | 30.86 % |  |
| 63.63 % | 69.24 % | + 8.82 % |

**TEST**

**NON-TEST**

## Conclusions

- Average size of warnings increased slightly (why?)
- Areal percentage of counties decreased overall
- 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