Using Short Range Ensemble Model Data in National Fire Weather Outlooks

Sarah J. TaylorDavid Bright, Greg Carbin, Phillip Bothwell

NWS/Storm Prediction Center

Richard NadenSouthwest Predictive Services

Overview

• SPC Fire Weather Program• Use of short range ensemble forecasts (SREF)• Case Studies

• July 8, 2003

• Recent Santa Ana event (October 25-31, 2003)

• Conclusions

SPC Fire Weather Program

• Fire weather forecasts began in 1998

• Purpose is to provide national fire weather guidance to NWS, federal, state and local government agencies

• Product will outlook areas where critical fire weather conditions combined with pre-existing fuel conditions forecast to occur

• Critical Fire Weather Areas

• Extremely Critical Fire Weather Areas

• Dry Thunderstorm Areas– Issued for widespread dry lightning

SPC Fire Weather ProgramTypes of Outlooks:

Critical Fire Weather Area

• Outlooks based on forecasts of Relative Humidity, maximum temperatures, sustained winds, and pre-existing fuels– RH criteria varies by geography– Temperatures must be greater than 60 F– Sustained surface winds (10 meter) must be

greater than 20 mph– High Fire Danger Class Index, low 100/1000 hr

fuel moisture, long term drought

SPC Fire Weather Outlook Issued on Sunday October 26, 2003

Use of SREF output

• What is an ensemble forecast??– Collection of different model solutions– By changing the initial conditions, different

forecast solutions are created

• SPC uses a 15 member ensemble from NCEP– Consists of Eta, Eta KF, RSM models– 48 km resolution

Use of SREF output

• Ensemble forecasts first applied operationally in the 1990s

• Studies have shown that ensembles are more skillful than using 1 single model (Wandishin et al, 2001, Bright and Mullen 2001)

• SPC began using SREF operationally in 2002

Use of SREF output

• At the SPC, nearly 300 SREF products are available:– Relative Humidity

– Temperature

– Wind

– Fosberg Fire Weather Index

– Haines Index

– Convective precipitation

– Combinations of the above

Use of SREF outputStatistical Fields

• Mean and Spread– Shows the “average” of the ensemble– Will smooth small scale features

• Probability– Indicate the percentage of ensemble members

which meet certain criteria

• Extreme values– Useful in predicting “worst case” events

Fosberg Fire Weather Index Mean and Standard Deviation Valid July 8 at 2100 UTC

Probability of Fosberg FWI greater than 75Probability of Fosberg FWI greater than 50

Maximum Fosberg Fire Weather Index valid 18 UTC July 8, 2003

Case Studies/Verification

• SPC Fosberg Fire Weather Index is used to verify fire weather outlooks

• Index is calculated with local objective analysis scheme

• Fosberg FWI greater than 50 is a “threshold” value

Case Studies (July 8, 2003)

Forecast valid at 18 UTC on July 8

Minimum RH with Mean Surface Wind

Sustained winds 20 kts or greaterMinimum RH less than 5%

Maximum Fosberg Fire Weather Index valid 18 UTC

Observed maximum Fosberg FWI - valid 2100 UTC July 8, 2003

Santa Ana Event October 2003

• Statewide loss of 20 lives

• 2600 houses with over 725,000 acres burned

• Monetary loss figures for the disaster are estimated to be over two billion dollars

Satellite Loop

Image courtesy of Liam Gumley, Space Science and Engineering Center, UW-Madison

2055 UTC October 27, 2003

Loop runs from 18 UTC October 26- 00 UTC October 27

Loop runs from 18 UTC October 26- 00 UTC October 27

Loop runs from 18 UTC October 26- 00 UTC October 27

Santa Ana Event October 2003

• SREF showed some skill

• Increased resolution of model would likely create better forecasts

• Fosberg Fire Weather Index did not verify well for this event

Conclusions

• Short range ensemble forecasts will be used more and more in the future

• With increased experience and development, ensembles will likely prove to be more useful than a single deterministic model

Conclusions (Continued)

• Model resolution increases

• Better model physics

• Ongoing research in Initial Condition perturbations

• Increased ensemble spread

• Data mining tools and display

Acknowledgements

• The authors would like to thank Steve Weiss at the Storm Prediction Center for his review and Jason Levit for his assistance with case study data

For more information

• Visit the SPC Fire Weather Page:– www.spc.noaa.gov/fire– Page contains latest SPC fire outlooks, Eta forecasts

and latest surface analysis – Will include ensemble forecast guidance in the future– This presentation is available online:

www.spc.noaa.gov/publications/taylor/srefams.html

Email: Sarah.Taylor@noaa.gov