Operational Application of Ensembles at the SPC: Fire Weather Forecasting Where Americas Climate and Weather Services Begin David Bright NOAA/NWS/Storm Prediction Center Norman, OK Advanced Fire Weather Forecasters Course Fire Weather Virtual Conference April 25, 2008

Nine NWS National Centers

Hail, Wind, Tornadoes Excessive rainfall Fire weather Winter weather STORM 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 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

Example: A deterministic approach 57h NAM Forecast valid 21 UTC 25 June m Wind (> 15 mph); 2m RH (< 20%) (filled)

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

57h NAM Forecast Valid: 21 UTC 25 June 2007 Verifying Analysis Observed: 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 Example: A deterministic approach

Sources of Uncertainty in NWP: Observations –Density –Error –Representative –QC Analysis Models LBCs, etc. Satellite Land Data and Models

Uncertainty in Initial Analyses NCEP Eta Data Assimilation 850 mb Initial Analysis (Hgt, Tmp, Wnd) 20 March UTC NCEP WRF Data Assimilation 850 mb Initial Analysis (Hgt, Tmp, Wnd) 20 March UTC Two state of the art assimilation systems, and two similar but clearly different analyses (even over land).

500 mb Hgt RMSE – Winter 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: 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!

ModelRes Levels Mems Cld PhysicsConvection GFS 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

ModelRes Levels Mems Cld PhysicsConvection GEM ~100 km Sundqvist (mixed) Mixed North American Ensemble Forecast System (NAEFS) ModelRes Levels Mems Cld PhysicsConvection GFS T126* (~ 105 km) 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 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 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 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 Motivation for Ensemble Forecasting SPC Ensemble Applications in Fire Weather –Medium to Short-range Case Study (Southern California Fires Oct. 2007)  Focus on Sunday afternoon: 00Z 22 Oct 2007 Ensemble Calibration and Decision Support Summary and Future Directions

Day - 8 (Sunday Oct, ) 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) 192h Forecast Valid 00 UTC 22 Oct 2007

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

GEM GFS NCEPE015 GEMEN009 Control NAEFS Postage Stamp (Subset!) 500 mb Height

192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD) Ens Mean – Climatology Climate Spread Departure =

192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; mb Thickness; 10m Wind (mph)

192h Forecast Valid 00 UTC 22 Oct 2007 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, ) 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 Ensemble 00Z 16 October 2007 (Forecast hour = 144)

144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; mb Thickness; 10m Wind (mph)

144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation Windy, dry airmass

Day - 5 (Wednesday Oct, ) Satellite image on October 24, 2007 Key Points: Relatively high confidence in western ridge and offshore / Santa Ana wind event Ensemble 00Z 17 October 2007 (Forecast hour = 120)

120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; mb Thickness; 10m Wind (mph)

120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation 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, ) A helicopter scoops water from a golf course in Valencia, California AP Photo/Kevork Djansezian Key Points: Strong western ridge (ensemble mean +2 SD) Uncertainty in location/strength of trough, but mdt-stg Santa Ana likely Ensemble 00Z 18 October 2007 (Forecast hour = 96)

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height (m) and its Standard Deviation

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height (m) and its climatologically normalized SD Ensemble Spread Climate Spread Normalized Spread =

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; mb Thickness; 10m Wind (mph)

096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation 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, ) A back fire on a hillside in Jamul, California AP 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 Website

SREF 500 mb Mean Height, Wind, Temp

SREF 500 mb Height (Spaghetti = 5700 m)

SREF Mean PMSL, 10m Wind, Thickness

SREF 10 meter Maximum Wind (any member)

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

SREF 700 mb Mean Wind (kts)

SREF Mean 2m Dew Point Temperature

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

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

SREF Minimum RH (any member)

Pr [P12I < 0.01”] X Pr [RH < 15%] X Pr [WSPD > 20 mph] X Pr [TMPF > 60F] SREF Combined or Joint Probability Critical Conditions

SREF Combined or Joint Probability Pr [P12I < 0.01”] X Pr [RH < 15%] X Pr [WSPD > 30 mph] X Pr [TMPF > 60F] High-end Critical Conditions

SREF Combined or Joint Probability Pr [P12I < 0.01”] X Pr [RH < 10%] X Pr [WSPD > 30 mph] X Pr [TMPF > 60F] 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 > 60] and Mean FFWI = 60

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

SREF Maximum Fosberg Index (any member) Extreme values

Examine the Individual Member Forecasts (Plumes)

2m Relative Humidity Plumes Clustering by model Good agreement RH ~5-10%

10m Wind Speed Plumes Sustained winds 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, )...DISCUSSION... …EXTREMELY CRITICAL FIRE WEATHER AREA - MTNS/VALLEYS OF SRN CA… PRIMARY CONDITIONS: SUSTAINED NELY WINDS FROM 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 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

Calibrated Probability of a Thunderstorm 15h Forecast Ending: 00 UTC 01 Sept 2004 Calibrated probability: Solid/Filled 3 hr valid period: 21 UTC 31 Aug to 00 UTC 01 Sept 2004

15h Forecast Ending: 00 UTC 01 Sept 2004 Calibrated 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

Perfect Forecast No Skill Perfect Forecast No Skill Calibrated Reliability (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 UTC 15 June 2006

SREF 3h Calibrated Probability of “Dry” Thunderstorms Dry thunderstorms = CG Lightning with < 0.10” precipitation 27 hour SREF Guidance Valid UTC 15 June 2006 Red indicates grid cells with “dry lightning”

SPC SREF Web Page Calibrated Guidance Plume Site

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

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 ENSEMBLEINPUTSENSEMBLEINPUTS

SPC Fire Outlooks on the WEB

SPC SREF Products on the WEB Questions/Comments…