# Presentation: 519063

## National Weather Service

**Polygons: A Practical Approach to Sub County Warnings  **

**National Severe Weather Workshop  **
**March 3, 2005**** **
**Richard Okulski**
**NOAA/NWS Severe Weather Program Leader**** **

## Overview 

**History of Sub County Warnings  **
**Polygons  **
**Valid Time Event Code (VTEC)    **
**Preliminary Local Storm Reports (LSRs) **
**Practical Application of Polygons, VTEC and LSRs**
**Where Are We Now?**
**Where Are We Heading?**
**Questions   **
** **

## History of Sub County Warnings

**Sub County LAT/LON Information in Short Duration Warnings Since the Late 1990s**
**LAT/LON Added to Follow Up Statements (e.g. Severe Weather Statement) in 2002 **
**Whole County Warnings Problematic for the Western U.S.  **
***Coconino County, AZ is larger than several small Eastern states ***
**Areas are Warned Which Are Not Threatened by Severe Weather and/or Flash Flooding **

## Polygons

**What are Polygons in NOAA Products and Services?**
***A Series of at Least Four Latitude/Longitude Point Pairs Found at the Bottom of all Text Severe Thunderstorm, Tornado, Special Marine and Flash Flood Warnings and Associated Follow Up Statements  ***
***Currently Defines the Area of Maximum Impact in a Warned County or Marine Zone ***
***Provides Warning Information at the Sub County/Marine Zone Level ***
***LAT/LON Point Pairs Are Easily Plotted in a Graphical Format  ***

## Valid Time Event Code (VTEC)     

**New Event Specific Dissemination Code **
**Mandatory for all Severe Thunderstorm, Tornado, and Special Marine Warnings and Associated Follow Up Statements    **
**Information Encoded in VTEC:   **
***Event Type and Significance   ***
***Start and End Times****** ***
***Whether Event is a Test, Operational or Experimental  ***
***Event Tracking Number (ETN)***
**Each Event has its Own Unique ETN For a Combination of Type/Significance (e.g. Severe Thunderstorm Warning,  Special Marine Warning)**

## Severe Thunderstorm Warning 

- SVREWX
- TXC285-240315-
- /O.NEW.KEWX.SV.W.0039.041124T0228Z-041124T0315Z/  (VALID TIME EVENT CODE)
- BULLETIN - EAS ACTIVATION REQUESTED
- SEVERE THUNDERSTORM WARNING
- NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
- 828 PM CST TUE NOV 23 2004
- THE NATIONAL WEATHER SERVICE IN AUSTIN SAN ANTONIO HAS ISSUED A
- * SEVERE THUNDERSTORM WARNING FOR THE FOLLOWING COUNTIES...
-   LAVACA
- * UNTIL 915 PM CST
- * AT 830 PM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
-   SEVERE THUNDERSTORM CAPABLE OF PRODUCING NICKEL SIZE HAIL...AND
-   DAMAGING WINDS IN EXCESS OF 60 MPH.  THIS STORM WAS LOCATED 8 MILES
-   SOUTHWEST OF HALLETTSVILLE...AND MOVING EAST AT 35 MPH.
- * OTHER LOCATIONS IN THE WARNING INCLUDE EZZELL AND SUBLIME.
- LAT...LON 2942 9719 2912 9692 2934 9661 2961 9687  (POLYGON LATITUDE AND LONGITUDE VERTICES)
-                   2961 9715
- $$

**Severe Thunderstorm Warning **

## Severe Weather Statement 

- SEVERE WEATHER STATEMENT
- NATIONAL WEATHER SERVICE JACKSON MS
- 646 AM CST THU DEC 9 2004
- MSC065-091256-
- JEFFERSON DAVIS MS-
- /O.CAN.KJAN.SV.W.0045.000000T12091300Z/
- 646 AM CST THU DEC 9 2004
- ...THE TORNADO WARNING FOR JEFFERSON DAVIS COUNTY IS CANCELLED...
- LAT...LON 3160 8962 3145 8956 3146 8941 3165 8940
- $$
- MSC031-091300-
- COVINGTON MS-
- /O.CON.KJAN.SV.W.0045.000000T12091300Z/
- 646 AM CST THU DEC 9 2004
- ...A TORNADO WARNING CONTINUES UNTIL 700 AM CST FOR COVINGTON
- COUNTY...
- AT 641 AM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
- INDICATE A TORNADO.  THIS TORNADO WAS LOCATED NEAR SEMINARY...OR
- ABOUT 10 MILES SOUTH OF COLLINS...MOVING EAST AT 40 MPH.
- THE TORNADO WILL BE NEAR...
-   SANFORD AND SEMINARY BY 645 AM CST
- LAT...LON 3160 8962 3145 8956 3146 8941 3165 8940
- $$

**Severe Weather Statement **

## Preliminary Local Storm Reports (LSR)    

**Preliminary Documentation of Warning Criteria Events        **
***Received from Spotters, Law Enforcement, Media   ***
**Disseminated to the Public Shortly After Reports are Received   **
***Event Type      ***
***Time of Event******   ***
***Who Reported the Event (e.g. Spotter)  ***
***LAT/LON Point of Where the Event Occurred****** ******  ***
**Graphical Display of LSR Reports Will Show Whether an Event Occurred Within the Polygon! **

## PRELIMINARY LOCAL STORM REPORT

- NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
- 351 PM CST TUE NOV 23 2004
- ..TIME...      ...EVENT...           ...CITY LOCATION...               ...LAT.LON...
- ..DATE...     ....MAG....             ..COUNTY LOCATION...ST.. ...SOURCE....
-                     ..REMARKS..
- 0115 PM      HAIL                  MIDWAY                                   31.03N 95.75W
- 11/23/2004   1.75 INCH        MADISON                         TX   AMATEUR RADIO
-                      FM1119 1.5 MILES NORTH OF OSR
- 0220 PM     TORNADO            BRENHAM                            30.16N 96.40W
- 11/23/2004                                WASHINGTON             TX   LAW ENFORCEMENT
-                     MARBLE SIZED HAIL ALSO REPORTED.
- 0220 PM     TSTM WND DMG  BRENHAM                           30.16N 96.40W
- 11/23/2004                                WASHINGTON             TX   LAW ENFORCEMENT
-                     TREES DOWN.
- 0240 PM     HAIL                      BRENHAM                            30.16N 96.40W
- 11/23/2004  1.75 INCH            WASHINGTON              TX   LAW ENFORCEMENT
-                    SOUTH SIDE OF TOWN.
- 0325 PM     TORNADO           TODD MISSION                    30.26N 95.83W
- 11/23/2004                              GRIMES                          TX  LAW ENFORCEMENT
-             POSSIBLE TORNADO IN TOWN.
- &&
- $$

## Practical Approach to Sub County Warnings    

**Parse Warnings and Follow Up Statements for the Following Information         **
***LAT/LON Point Pairs (Sub County Warning Location)***
***Event Start and End Time ***
***Valid Time Event Code (Event Type and Tracking Number)   ***
**Parse Local Preliminary Local Storm Reports    **
***Event Type      ***
***Time of Event   ***
***LAT/LON Point of Where the Event Occurred ******  ***
**Overlay of Events and Warning Polygons Results in Near Real Time Verification (Right Time and Place) **

## Sub County Warning Case #1    

**January 13, 2005**
**Western Missouri (WFOs Springfield and Pleasant Hill) **
**Severe Thunderstorm Warnings and Severe Weather Statements Issued **
**LSRs issued to Report Tornadoes, Large Hail and Damaging Wind **
**What Did this Event Look Like Using a Polygon Approach?  **

## Case #1: Polygons/Event Reports 

## Sub County Warning Case #2    

**February 13, 2005**
**East Texas and Western Louisiana (WFOs Houston and Shreveport) **
**Severe Thunderstorm Warnings and Severe Weather Statements Issued **
**LSRs issued to Report Large Hail **
**What Did this Event Look Like Using a Polygon Approach?  **

## Case #2: Polygons/Event Reports 

## Where Are We Now?

**Polygon Demonstration at 22 WFOs from March 1 to September 30 **
**Goal: Finer Resolution Warnings (Below the County Level)  **
**Operational VTEC in Severe Thunderstorm, Tornado and Special Marine Warnings  **
**Polygon Definition: Area of Maximum Impact Within a Warned County **
**NOAA Still Uses A County Based Warning System **

## Where Are We Heading?

**The Polygon is the Warning! (Target: Fall 2006)     **
**VTEC in Most NOAA Watches, Warnings and Advisories**
**Other Candidate Products for the Polygon Approach**
***Convective Watches ***
***Flood Watches ***
**Reasons for Change**
***Reduce False Alarm Area in Warnings ***
***Finer Resolution Warnings ***

## Questions? 

**For More Information on Polygons:**
**	****www.nws.noaa.gov/os/polygon**
**     **