# Presentation: 529374

##  Evolving to Polygon Warnings:An Effective False Alarm Solutionfor the National Weather Service  

- Pete Wolf, SOO
- NWS Jacksonville FL

**Notes:**
“With Polygon Warnings, we’re going to reduce tornado warning false alarms by at least 50%, with minimal impact on POD. This presentation focuses on this goal, and how we’ll get there through the polygon warning approach, as well as the SOOs’ role in this evolution.”

## False Alarms

**Two Key Types:**
**“****Unavoidable” FA’s**
- “FIRE!”, with smoke pouring into             the room.
- Our mission requires warnings,     regardless of verification.
**“****Unnecessary” FA’s**
- “FIRE!”, with no smoke or fire                   (no actual threat).
- This is what we aim to reduce with    polygon warnings.
**False Alarms are a Factor.**
- Affect credibility, thus response.

**Notes:**
“There are actually two types of false alarms to consider.”

## Options for Reducing False Alarms

**Option #1**: Issue fewer warnings ***(GPRA FAR goal*****)**
- Change warning methodology that leads to fewer warning issuances (e.g. only strong meso or TVS for tornado warnings).
- For 3000/4000 unverified warnings...FAR = 0.75
- For 2300/3300 unverified warnings...FAR = 0.70    ***(GPRA met)***
- For 1500/2500 unverified warnings...FAR = 0.60
- Risk of significant unwarned events **increases**.
- Harold Brooks presented POD-FAR relationship.
- A “_**bad idea**_” from “risk management” perspective.
**Option #2**: Issue smaller warnings
- Can reduce false alarm area by 50% or more.
- Still issue warnings for perceived threats.
- From “risk management” perspective, this is a
-    _**much better idea**_.

**Notes:**
“The primary option for meeting the GPRA FAR goal is to issue fewer warnings.  The goal for TORs is simply to reduce FAR from about 0.75 to 0.70 over 5 years. At the surface, that doesn’t seem too difficult. However the number of false alarms to be reduced to meet that goal may seem surprising.”

## Polygon Warning Defined

- Simply put, a polygon warning (PW) is the the following:
- PW = WCW – FAA *(“unnecessary”)*
- where WCW is the whole county warning and FAA is the
- area where no perceived imminent threat exists.

-  -                    =

- In the polygon approach, all we’re trying to do is reduce
- alerted territory where no imminent threat is perceived.

**Notes:**
“All we’re trying to do in the polygon approach is to reduce the amount of ‘unnecessary’ FAA in our warnings...that’s all.”

## FAR vs FAA (Not the Same Thing!)

**# FAs      Average FA size        Total FAA**
-  1000         800 sq mi each       800,000 sq mi
-  1500         266 sq mi each       400,000 sq mi

- If you** increase** FA’s from 1000 to 1500, you **increase** your FAR by 50%. But, at the same time, if you **reduce** average warning size from 800 sq mi to 270 sq mi each (1/3 original size), you actually **decrease** FAA by 50%.
- In a national county- vs polygon-based warning study, from 2004 to 2005,
- FAA **decreased** by about 10%, despite a year-to-year **increase** in FAR.
** **

## Comparing Counties to Polygons

- Field evaluation was completed in 2005.
- Involved over 20 WFOs across the country.
- Results confirmed those from local studies at Wichita and Jacksonville.
- 70% reduction in TOR FAA with polygon warnings compared to whole-county warnings.
- Larger in WR offices, smaller in ER offices.
- Reduction is “unnecessary” false alarm area.
- Some negative impact on POD.
- More so than anticipated based on concept.
- Training and software issues.

**                 ****T**
** ****T**

## Polygon Warning Issues

**Issue #1:** Describing polygon aerial coverage
-    for text products/audio broadcasts (NWR).
- Text products will look similar to today.
- Likely will shift focus from “pathcasts” to “locations
-    in warning” in text product.
- Any issues due to polygons also exist today
-     with partial county warnings.

**A   ****	****B****	**** G****	****  H**
**C****	****D****	****  I****	****  J**
**E****	****F****	**** K ****	****  L**

- #1                #2

## What do we provide today?

**The National Weather Service in Jacksonville has issued a... **
**Severe Thunderstorm Warning for the following locations...**
**Southern Nassau County in Northeast Florida**
**Western Duval County in Northeast Florida**
**Northern Clay County in Northeast Florida**
**until 700 pm EST.**
**At 610 pm EST...Doppler Radar indicated a line of severe**
**thunderstorms extending from 6 miles southweest of St. George to near Baldwin to 7 miles south of Lawtey...or extending from 15 miles west of Callahan to 18 miles west of Downtown Jacksonville to 15 miles southwest of Middleburg...moving east at 40 mph. The storms are capable of producing damaging winds up to 60 mph, heavy rainfall and deadly cloud-to-ground lightning.**
**The storms will be near...**
**Bryceville at 620 pm EST**
**Nassau Village and Jacksonville Heights at 635 pm EST**
**Jacksonville International Airport at 650 pm EST**
**Riverside at 655 pm EST**
**This is a dangerous line of storms...with a history of producing damaging winds. Take cover now! **

## Polygon Warning Issues

**Issue #2:** How will we verify polygon warnings?
- Shift to polygon-based verification (including GPRA measures) planned by FY08.
- WFOs will be encouraged to shift from counties to polygons in FY07.
- Concern about Polygon-based FAR leading to larger polygons and more FAA (not less FAA). Polygon size needs to be incorporated.
- Report accuracy is critical to for polygon warning verification.
- Will increase post-event work.

- TORNADO
- WARNING

## Polygon Warning Issues

**Issue #3:** Software
- Private Sector: game of “chicken”    ...who goes first?
- Technology companies may wait until NWS shifts to polygons before upgrading their technology
- NWS may be waiting to shift to polygons until private companies upgrade their technology.
- After the NWS takes the lead, the private sector will rapidly follow.
- Who wants to be the only one not providing polygon warnings?
- NWS:
- WarnGen
- LSR
- Changes in support of polygon warnings are planned in OB8 (Spring/Summer ’07)

## Polygon Warning Issues

**Issue #4:** Forecaster Training...“Polygonology”
- Areas in gap between polygons are **not warned**.
- Overlap not as critical of a problem but should be minimized as much as possible.
- County borders are not important, but CWA borders are!
- Confusion from issuing too many warnings.
- Dealing with multiple threats.

- What single change could you make today at your WFO to get us started in the right direction?

**Notes:**
SR supercell case...thru 3pm....~56 whole county alerts, ~26 polygons, ~16-19 needed threat-based polygons.

## Avoid Drawing Whole County Polygons 

**Stop drawing polygons to match county borders**!
- Let the polygons outline the threat areas.
* **(Let’s r**eview an interesting sr-supercell case...March 12, 2006.)*

## Warning-By-Polygon Benefits

- Focus warning on the true threat area
- Reduce the area alerted that’s not threatened
- Easier handling storms moving along county borders
- Supports weather radio evolution to
-     alert areas smaller than county
- Supports efforts to warn on smaller
-     events we may typically miss/ignore.
- Supports development of graphical/web
-     based products that show threat area.

## Probabilistic Guidance: The Next Step Beyond Polygon Warnings

**Case #1: Central Mississippi, April 6, 2003**
- Major severe weather event during the afternoon/early evening hours.

- Blue Polygon: *Low Probability*
*(warning may be needed if further intensification/advection occurs)*
- Magenta Polygon: *High Probability*
*(deterministic warning polygon)*
- (_**Note**_: focus is just on “damaging weather”, not tornado vs wind vs hail.)

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**P A U S E**

## Probabilistic Guidance: The Next Step Beyond Polygon Warnings

**Case #2: Northern Florida, June 16, 2005**
- Strong (isolated severe) pulse t-storms during the afternoon.**  **

- Green Polygon: *Low Probability*
*(warning may be needed if further intensification/advection occurs)*
- Magenta Polygon: *High Probability*
*(deterministic warning polygon)*

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- SVR issued for Suwannee Co

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- SVR issued for Suwannee Co

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- SVR issued for Suwannee Co

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County

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- SVR issued for St. Johns County          P A U S E

## Latest Polygon Warning Implementation Information

- Polygon Evaluation Team                     Polygon Implementation Team
- Approved by Ops. Committee of Corporate Board
- Forecaster Training                               Planned through CY07
- Intro concept module/teletraining
- WES-based scenario training
- Needed software improvements           Planned starting in OB8 (CY07)
- Operational implementation**	****  ****	****  Planned for FY08**
- Implementation of polygon 		  **Planned for FY08**
-      verification in GPRA**	****	**** ****	****  **

## Final Thought

***“******One doesn’t discover new lands without***
***  ******consenting to lose sight of the shore for ***
***  ******a very long time.”         *****          **--- Andre Gide

- Any thoughts/questions?
-         Pete Wolf, SOO
-      NWS Jacksonville FL