# Presentation: 169168

## Tornado and Severe Thunderstorm Watches

**Conditions favor the development of **_**organized intense convection**_
**over a multiple-WFO region (25,000 - 30,000 mi****2****)**
**- Objective -**** **
**Alert NWS partners/customers to monitor conditions **
**because of enhanced potential for severe storms**

**Tornado and Severe Thunderstorm Watches**
**- not envisioned as a call to take explicit precautions -****  **

## Tornado Watch Lead Time (1970-2007)

**Tornado Watch Lead Time (1970-2007)**

**~ 68% within ± ****σ**** of mean**

## Tornado Watch Area (1970-2007)

**Tornado Watch Area (1970-2007)**

**~ 68% within ± 1****σ**** of mean**

## Watch type, size, lead time are a function of the meteorology

***Watch type, size, lead time are a function of the meteorology***
***Policies that have arisen from Partner’s Concerns***

-   **Attempt to issue watches before a WFO starts posting warnings**
**  ****Minimize watches affecting any given WFO area**
**                 ****If multiple storm periods are expected -- issue one long watch**
**                 ****Use long watch for Tropical Storm related events**
** **
**  ****Attempt to issue overnight watches before nightly news ****(9pm-11pm)**
**  ****Collaborate with ****WFOs on ****counties included, duration, and issue time**
**   ****Watches are valid when issued**

## Factors arguing for Shorter Watches

***Factors arguing for Shorter Watches***
**   ****Emergency Operations Centers activated (overtime incurred)**
**   ****Shelters staffed and opened to public**** **
***                  ******Message - take shelter early; do not wait until a warning is issued***
**   ****Emergency responders on stand-by (volunteers may leave primary jobs)**
** **

***Factors arguing for Longer Watches***
**   ****Hospital staff put on stand-by (additional staffing may be arranged)**
**   ****Industries may activate emergency plans (add or reduce staffing/shifts)**
**   ****Aviation Interests need anticipated destination conditions before departure**
**   ****Goal of “Warn-on-Forecast” is one hour Warning Lead Time**

## Potential Compromise 

**In 1999, the Partners requested that **
**              ****Watches become valid when issued.**
**Should the NWS consider reinstituting a **
**         ****Watch valid time different from its issue time?**

**Potential Compromise**** **
**Use a valid time that is later than the issue time**

## Backup Slide

**                              ****Tornado        Severe Tstm.      **
**Number                     291                    612                    **
**Size ( n-mi****2****)           24,904               23,983****               **
**# of Counties             52                      45****                     **
**Duration                   6’37”                  6’03”**
**Lead Time            Tornado          Severe Tstm.      Any Watch**
**    ****To Tornado          2’12”                   2’17”                 2’14”     **
**        ****by County        3’03”                   2’40”                 2’57”**
**    ****To any Severe     1’10”                      53”                    58”   **
**        ****by County        2’52”                   2’22”                 2’33”**

**Backup Slide**