Operational Application of Ensembles at the SPC: Fire Weather Forecasting Where Americas Climate and Weather Services Begin David Bright NOAA/NWS/Storm

Operational Application of Operational Application of Ensembles at the SPC:Ensembles at the SPC:

Fire Weather ForecastingFire Weather Forecasting

Where Americas Climate and Weather Services Begin

David BrightNOAA/NWS/Storm Prediction Center

Norman, OK

Advanced Fire Weather Forecasters CourseFire Weather Virtual Conference

April 25, 2008

Nine NWS National Centers

• Hail, Wind, Tornadoes

• Excessive rainfall

• Fire weather

• Winter weather

STORM PREDICTION CENTERSTORM PREDICTION CENTER HAZARDOUS PHENOMENA

SPC Fire Weather Outlooks• To provide national fire weather guidance for use by the National

Weather Service, as well as other federal, state, and local government agencies

• The products are intended to delineate areas of the contiguous U. S. where the forecast weather conditions, combined with pre-existing fuel conditions, result in a significant threat for wildfires

• Issued once per day during the overnight hours (through 8 days)

• Critical, Extremely Critical, and Critical Dry Thunderstorm forecasts– Low RH– Moderate / strong winds– Antecedent conditions / drought (NFDRS)– Critical area for dry thunderstorms implies

widespread lightning with minimal rainfall

Outline

• Motivation for Ensemble Forecasting

• SPC Ensemble Applications in Fire Weather– Medium to Short-range Case Study

(Southern California Fires Oct. 2007)

• Ensemble Calibration and Decision Support

• Summary and Future Directions

Outline






Example: A deterministic approachExample: A deterministic approach

57h NAM Forecast valid 21 UTC 25 June 200710m Wind (> 15 mph); 2m RH (< 20%) (filled)


Truth: SPC OA valid 21 UTC 25 June 200710m Wind (> 15 mph); 2m RH (< 20%) (filled)

57h NAM Forecast Valid: 21 UTC 25 June 2007

Verifying AnalysisObserved: 21 UTC 25 June 2007

• Does not provide direct information on forecast uncertainty• Could be misleading and oversell forecast capability• Decision making may be optimized by considering uncertainty


??

Sources of Uncertainty in NWP:Sources of Uncertainty in NWP:

• Observations– Density– Error– Representative– QC

• Analysis• Models • LBCs, etc.

Satellite

Land

Data and Models

Uncertainty in Initial AnalysesUncertainty in Initial Analyses

NCEP Eta Data Assimilation850 mb Initial Analysis (Hgt, Tmp, Wnd)

20 March 2006 12 UTC

NCEP WRF Data Assimilation850 mb Initial Analysis (Hgt, Tmp, Wnd)

20 March 2006 12 UTC

Two state of the art assimilation systems, and two similar but clearly different analyses (even over land).

500 mb Hgt RMSE – Winter 2006-2007

Slope of Ens Mean (solid) is less steep

Skill is retained longer

Same results in summer

Deterministic models lose skill faster than ensemble mean

Ens Spread

Ens Mean

GFS and Ens Control

Climatology

Ens mean reduces RMSE after Day 3. Improvement increases with time and extends predictability Spread-skill

suggests ensemble is underdispersive

Error Growth with Time: GFSError Growth with Time: GFS

1.41 x Climate RMSE

(Limit of Skill)

Ensemble skill ~12-13 daysDeterministic skill ~10 days

- Weather models...- All forecasts contain errors that

increase with time- Doubling time of small initial errors ~1

to 2 days- Maximum large-scale (synoptic to

planetary) predictability ~10 to 14 days

- Ensemble systems…- A collection of models that provide

information on the range of plausible forecasts and extend predictability

- Increasing in popularity- Principles scale (global high-res)- Requires “tools” to view the large

number of models using a slightly different approach (statistical)

Weather forecasting: It’s impossible to be deterministically correct all of the time!

Model Res Levels Mems Cld Physics ConvectionGFS T126* (~ 105 km) 28 20** GFS physics Simple A-S

* Same as the operational GFS in 1998** 20 statistically independent perturbations (using Ensemble Kalman filter method)

NWS/NCEP Global Ensemble Forecast System (GEFS; the

ensemble formerly known as MREF)

Ensembles Available at the SPC: GEFS

Four times per day: 00, 06, 12, 18 UTC

Model Res Levels Mems Cld Physics ConvectionGEM ~100 km 28 20 Sundqvist (mixed) Mixed

North American Ensemble Forecast System (NAEFS)

Model Res Levels Mems Cld Physics ConvectionGFS T126* (~ 105 km) 28 20 GFS physics Simple A-S

NAEFS was launched in 2004 as a joint experimental project between the U.S. National Weather Service, Meteorological Service of Canada, and the

National Meteorological Service of Mexico.

Advantages to combining two state-of-the-art ensemble systems:• Increase spread through more members and inclusion of model uncertainty• Provides seamless forecast guidance across national borders• Allows for cost sharing of research, development, and maintenance costs

http://www.weatheroffice.gc.ca/ensemble/index_naefs_e.html

Ensembles Available at the SPC: NAEFS

NWS/NCEP Short Range Ensemble Forecast (SREF)

• EMC SREF system (21 members)– 87 hr forecasts four times daily (03, 09, 15, 21 UTC)

– North American domain

– Model grid lengths 32-45 km

– Multi-model: Eta, RSM, WRF-NMM, WRF-ARW

– Multi-analysis: NAM, GFS initial and boundary conds.

– IC perturbations and physics diversity

Ensembles Available at the SPC: SREF

Ensemble Guidance at the SPCEnsemble Guidance at the SPC

• Develop specialized guidance for the specific application (severe weather, fire weather, winter weather)

• Design guidance that…– Helps blend deterministic and ensemble approaches– Facilitates transition toward probabilistic forecasts– Considerable diagnostic parameter evaluation in probability

space– Aids in decision support of high impact

weather• Gauge confidence • Alert for potentially significant

events

Outline



(Southern California Fires Oct. 2007) Focus on Sunday afternoon: 00Z 22 Oct 2007



Day -8 (Sunday Oct, 14 2007)

Harris Fire burns on Mount San Miguel the morning of October 23, 2007

Key Points: Examine the large-scale synoptic weather pattern A couple of members indicate the potential of an offshore wind event

Ensemble 00Z 14 October 2007 (Forecast hour = 192)

GEFS Ensemble Mean: 500 mb Height and Vorticity

192h Forecast Valid 00 UTC 22 Oct 2007

GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)



GEM Ensemble Spaghetti: 500 mb Height (Single contour at 5700 m)

Verifying analysis

GEM

GFS

NCEPE015

GEMEN009 Control

Control

http://www.weatheroffice.gc.ca/ensemble/cartes_e.html#

NAEFS Postage Stamp (Subset!) 500 mb Height


GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

Ens Mean – ClimatologyClimate Spread

Departure =


GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)


GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

Breezy, dry airmass

...DISCUSSION... A BROAD UPPER TROUGH WILL DEEPEN FROM DAY 3 INTO DAY 5 AS IT

DEVELOPS OVER THE FOUR CORNERS AREA AND MOVES INTO THE PLAINS...RESULTING IN STORMY WEATHER. THE TROUGH PASSAGE WILL LIKELY RESULT IN STRONG WLY WINDS AND MODERATELY LOW RH ACROSS NM AND W TX ON DAY 5 10/18...BUT CRITICAL CONDITIONS ARE NOT EXPECTED.

PREDICTABILITY THEN DECREASES AFTER ABOUT DAY 4 AS MODELS DIFFER IN SPEED OF UPPER LOW/TROUGH THAT DEVELOPS OVER THE CNTRL U.S. DEGREE OF RIDGING BEHIND THIS TROUGH WILL DETERMINE HOW MUCH POTENTIAL THERE IS FOR OFFSHORE FLOW INTO SRN CA/AZ...MOST LIKELY TO OCCUR IN THE 10/19-10/20 TIME FRAME.

Day -6 (Tuesday Oct, 16 2007)

NASA satellite image of southern California on the afternoon of October 21, 2007

Key Points: Ensemble trend for strong western ridge continues Offshore flow pattern well established in the mean












Windy, dry airmass

Day -5 (Wednesday Oct, 17 2007)

Satellite image on October 24, 2007

Key Points: Relatively high confidence in western ridge and offshore / Santa Ana wind event












Windy, very dry airmass

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/ENSEMBLES SUGGEST THE

NEXT IN A SERIES OF UPPER TROUGHS WILL LIKELY CROSS THE WESTERN STATES THIS WEEKEND. MODEL CONCENSUS SUGGESTS THIS UPPER TROUGH MAY ULTIMATELY BECOME CUT-OFF OVER THE SOUTHWEST STATES...ALTHOUGH CONSIDERABLE DISCREPANCY EXISTS IN THE PLACEMENT DETAILS. REGARDLESS...IN THIS WAKE OF THIS SYSTEM...IT APPEARS AN OFFSHORE/SANTA ANA WIND EVENT MAY BECOME ESTABLISHED ACROSS SOUTHERN CA BY LATE DAY 4/SATURDAY AND DAY 5/SUNDAY INTO DAY 6/MONDAY. AS SUCH...THE POTENTIAL WOULD EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES.

Day -4 (Thursday Oct, 18 2007)

A helicopter scoops water from a golf course in Valencia, CaliforniaAP Photo/Kevork Djansezian

Key Points: Strong western ridge (ensemble mean +2 SD)Uncertainty in location/strength of trough, but mdt-stg Santa Ana likely







GEFS Ensemble: Mean 500 mb Height (m) and its climatologically normalized SD

Ensemble SpreadClimate Spread

Normalized Spread =







Very windy, very dry airmass

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/ENSEMBLES SUGGEST THE NEXT IN A

SERIES OF UPPER TROUGHS WILL LIKELY CROSS THE WESTERN STATES THIS WEEKEND. CONSIDERABLE MODEL DISCREPANCY EXISTS IN REGARDS TO THE PROGRESSION OF THIS SYSTEM...WITH THE 00Z EUROPEAN SUGGESTING THE TROUGH COULD BECOME CUT-OFF OVER THE SOUTHERN ROCKIES.

INITIALLY ON DAY 3/SATURDAY...STRONG GUSTY WINDS ASSOCIATED WITH THE UPPER TROUGH/STRONG JET COULD YIELD AT LEAST NEAR-CRITICAL CONDITIONS ACROSS THE SOUTH CENTRAL HIGH PLAINS. THEREAFTER...IN THE WAKE OF THE UPPER TROUGH...CONFIDENCE CONTINUES TO INCREASE THAT A MODERATE-STRONG OFFSHORE/SANTA ANA WIND EVENT MAY BECOME ESTABLISHED ACROSS SOUTHERN CA BY LATE DAY 3/SATURDAY AND DAY 4/SUNDAY THROUGH DAY 6/TUESDAY. AS SUCH...THE POTENTIAL WOULD EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES INTO EARLY NEXT WEEK.

Day -3 (Friday Oct, 19 2007)

A back fire on a hillside in Jamul, CaliforniaAP Photo/Kevork Djansezian

Key Points: Shift focus to the Short Range Ensemble Forecast (SREF) Begin to examine mesoscale details and diagnostics

AP Photo/Rick Bowmer

SREF Ensemble 21Z 18 October 2007 (Forecast hour = 75)

SREF Products Available on the SPC WebsiteSREF Products Available on the SPC Websitehttp://www.spc.noaa.gov/exper/sref/

SREF 500 mb Mean Height, Wind, Temp

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_H5__&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF 500 mb Height (Spaghetti = 5700 m)

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_Spaghetti_H5_5700__&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF Mean PMSL, 10m Wind, Thickness

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_PMSL_1000-500_THK_BLW_&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF 10 meter Maximum Wind (any member)

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_10M_WIND_MAX__&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF Pr[WSPD > 20 mph] and Mean WSPD = 20 mph (dash)

SREF 700 mb Mean Wind (kts)

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_wind_vector_700mb_&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF Mean 2m Dew Point Temperature

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_FIRE_DWPF_MEAN_&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF Pr[RH < 15%] and Mean RH = 15% (dash)

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_prob_FIRE_relh_lt15__&cur_dir=case_2007101821/&gifs_dir=./gifs/

SREF Pr[RH < 10%] and Mean RH = 10% (dash)

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_prob_FIRE_relh_lt10__&cur_dir=case_2007101821/&gifs_dir=./gifs/

Pr [P12I < 0.01”] XPr [RH < 15%] XPr [WSPD > 20 mph] XPr [TMPF > 60F]

SREF Combined or Joint Probability

Critical Conditions

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_COMBO_WSPD20_RH15__&cur_dir=case_2007101821/&gifs_dir=./gifs/



High-end Critical Conditions

http://spcwebsite.spc.noaa.gov/exper/sref/gifs/case_2007101821/loop.php?field=SREF_COMBO_WSPD30_RH15__&cur_dir=case_2007101821/&gifs_dir=./gifs/



Extremely Critical Conditions

SREF Median Fosberg Index + Union (red)Fosberg Fire Weather Index (FFWI)Non-linear, empirical relationship between weather and

fire behavior.

FFWI = F(Wind speed, RH, Temperature) 0 < FFWI < 100 FFWI > ~50-60 significant conditions FFWI > ~75 extreme conditions

Union: At least one member > 50

Median

SREF Pr[Fosberg Index > 70] and Mean FFWI = 70

SREF Maximum Fosberg Index (any member)

Extreme values

Examine the Individual Member Forecasts (Plumes)http://www.spc.nssl.noaa.gov/exper/sref/plume

2m Relative Humidity Plumes

Clustering by modelGood agreement RH ~5-10%

10m Wind Speed Plumes

Sustained winds 15-30 mph; clustered by model

Fosberg Fire Weather Index Plumes

FFWI values from 40-80; clustered by model; well over 50% > 60

...DISCUSSION... LATEST MEDIUM RANGE DETERMINISTIC MODELS/MREF ENSEMBLES CONTINUE TO

SUGGEST THAT THE NEXT UPPER TROUGH WILL CROSS THE WESTERN/CENTRAL STATES THROUGH DAY 3/SUNDAY...POSSIBLY BECOMING CUT-OFF/STALLING ACROSS THE SOUTHERN PLAINS EARLY NEXT WEEK. INITIALLY ON DAY 3/SUNDAY...STRONG GUSTY WINDS ASSOCIATED WITH THE UPPER TROUGH/STRONG JET COULD YIELD AT LEAST NEAR-CRITICAL CONDITIONS ACROSS THE SOUTH CENTRAL HIGH PLAINS.

AS HIGH PRESSURE PERSISTS ACROSS THE GREAT BASIN LATE THIS WEEKEND THROUGH EARLY NEXT WEEK...IT APPEARS A POTENTIALLY STRONG OFFSHORE/SANTA ANA WIND EVENT WILL OCCUR FROM EARLY DAY 3/SUNDAY INTO AT LEAST DAY 5/TUESDAY. THE POTENTIAL WILL EXIST FOR NOCTURNALLY-ENHANCED GUSTY WINDS ACROSS SOUTHERN CA...ALONG WITH WARMER TEMPERATURES AND LOWER RH VALUES THROUGH EARLY NEXT WEEK. THESE CONDITIONS...ALONG WITH EXTREME DROUGHT...SUGGEST A CONSIDERABLE FIRE DANGER WILL EXIST ACROSS SOUTHERN CA.

Day -2 (Saturday Oct, 20 2007)

...DISCUSSION... …EXTREMELY CRITICAL FIRE WEATHER AREA - MTNS/VALLEYS OF SRN CA…

PRIMARY CONDITIONS: SUSTAINED NELY WINDS FROM 30-50 MPH WITH GUSTS OVER 75 MPH...MIN RH READINGS FROM 5-10 PERCENT...LONG TERM DROUGHT A VERY STRONG SANTA ANA/OFFSHORE WIND EVENT IS EXPECTED TO DEVELOP BEGINNING LATE ON DAY ONE AND LASTING PAST DAY 2...

Outline






Calibrated Probability of a Thunderstorm Calibrated Probability of a Thunderstorm

15h Forecast Ending: 00 UTC 01 Sept 2004Calibrated probability: Solid/Filled

3 hr valid period: 21 UTC 31 Aug to 00 UTC 01 Sept 2004

15h Forecast Ending: 00 UTC 01 Sept 2004Calibrated probability: Solid/Filled; NLDN CG Strikes (Yellow +)

3 hr valid period: 21 UTC 31 Aug to 00 UTC 01 Sept 2004

Calibrated Probability of a Thunderstorm Calibrated Probability of a Thunderstorm

Perfect Forecast

No Skill

Perfect Forecast

No Skill

Calibrated ReliabilityCalibrated Reliability (5 Aug to 5 Nov 2004)(5 Aug to 5 Nov 2004)

Calibrated Thunder Probability

Climatology

Frequency[0%, 5%, …, 100%]

SREF 3h Calibrated Probability of Thunderstorms

Thunderstorm = > 1 CG Lightning Strike in 40 km grid box

What about dry thunderstorms?

Photo from John Saltenberger

27 hour SREF Guidance Valid 21-00 UTC 15 June 2006

SREF 3h Calibrated Probability of “Dry” Thunderstorms

Dry thunderstorms = CG Lightning with < 0.10” precipitation

27 hour SREF Guidance Valid 21-00 UTC 15 June 2006

Red indicates grid cells with “dry lightning”

SPC SREF Web Page

Calibrated Guidance

Plume Site

Outline






General Comments about Ensemble Approach at the SPC

• Ensembles have become a routine part of the forecast process at the SPC

• Ensemble approach to forecasting similar to the deterministic approach– Ingredients based inputs– Diagnostic and parameter evaluation– Tend to view diagnostics in probability space – particularly in short-range

• Ensembles contribute appropriate levels of confidence to the forecast process and can aid decision making (formally or informally)

• Calibration of ensemble output can remove systematic biases and improve the spread, and can be used to probabilistically downscale larger-scale environment

• Continue to enhance the short- and medium-range ensemble applications for the SPC fire weather program

– Expanded products in GEFS– Calibrated guidance– Incorporation of NAEFS– Collaboration with partners

Potential Fire Support From Ensembles

ENSEMBLE

INPUTS

SPC Fire Outlooks on the WEBSPC Fire Outlooks on the WEBhttp://www.spc.nssl.noaa.gov/products/fire_wx/overview.html

SPC SREF Products on the WEBSPC SREF Products on the WEBhttp://www.spc.noaa.gov/exper/sref/

Questions/Comments…[email protected]

Documents

Operational Application of Ensembles at the SPC: Fire Weather Forecasting Where Americas Climate and Weather Services Begin David Bright NOAA/NWS/Storm