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Operational Application of Ensembles at the SPC: Fire Weather Forecasting

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

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Operational Application of Ensembles at the SPC: Fire Weather Forecasting

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

  2. Nine NWS National Centers

  3. STORM PREDICTION CENTER HAZARDOUS PHENOMENA • Hail, Wind, Tornadoes • Excessive rainfall • Fire weather • Winter weather

  4. 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

  5. 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

  6. 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

  7. Example: A deterministic approach 57h NAM Forecast valid 21 UTC 25 June 2007 10m Wind (> 15 mph); 2m RH (< 20%) (filled)

  8. Example: A deterministic approach Truth: SPC OA valid 21 UTC 25 June 2007 10m Wind (> 15 mph); 2m RH (< 20%) (filled)

  9. Example: A deterministic approach ? 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

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

  11. Uncertainty in Initial Analyses NCEP Eta Data Assimilation 850 mb Initial Analysis (Hgt, Tmp, Wnd) 20 March 2006 12 UTC NCEP WRF Data Assimilation 850 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).

  12. Error Growth with Time: GFS 500 mb Hgt RMSE – Winter 2006-2007 1.41 x Climate RMSE (Limit of Skill) Deterministic skill ~10 days Ensemble skill ~12-13 days GFS and Ens Control Deterministic models lose skill faster than ensemble mean Climatology Slope of Ens Mean (solid) is less steep Skill is retained longer Same results in summer Ens mean reduces RMSE after Day 3. Improvement increases with time and extends predictability Ens Mean Ens Spread Spread-skill suggests ensemble is underdispersive

  13. 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!

  14. Ensembles Available at the SPC: GEFS NWS/NCEP Global Ensemble Forecast System (GEFS; the ensemble formerly known as MREF) Four times per day: 00, 06, 12, 18 UTC Model Res Levels Mems Cld Physics Convection 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)

  15. Ensembles Available at the SPC: NAEFS North American Ensemble Forecast System (NAEFS) 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 Model Res Levels Mems Cld Physics Convection GFS T126* (~ 105 km) 28 20 GFS physics Simple A-S Model Res Levels Mems Cld Physics Convection GEM ~100 km 28 20 Sundqvist (mixed) Mixed http://www.weatheroffice.gc.ca/ensemble/index_naefs_e.html

  16. Ensembles Available at the SPC: SREF 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

  17. 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

  18. 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

  19. Day -8 (Sunday Oct, 14 2007) Ensemble 00Z 14 October 2007 (Forecast hour = 192) 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

  20. 192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

  21. 192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

  22. 192h Forecast Valid 00 UTC 22 Oct 2007 Verifying analysis GEM Ensemble Spaghetti: 500 mb Height (Single contour at 5700 m)

  23. NAEFS Postage Stamp (Subset!) 500 mb Height GEM GEMEN009 Control GFS Control NCEPE015 http://www.weatheroffice.gc.ca/ensemble/cartes_e.html#

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

  25. 192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

  26. Breezy, dry airmass 192h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

  27. ...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.

  28. Day -6 (Tuesday Oct, 16 2007) Ensemble 00Z 16 October 2007 (Forecast hour = 144) 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

  29. 144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

  30. 144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

  31. 144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

  32. 144h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

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

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

  35. 120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

  36. 120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

  37. 120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

  38. 120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

  39. Windy, very dry airmass 120h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

  40. ...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.

  41. Day -4 (Thursday Oct, 18 2007) Ensemble 00Z 18 October 2007 (Forecast hour = 96) AP Photo/Kevork Djansezian A helicopter scoops water from a golf course in Valencia, California Key Points: Strong western ridge (ensemble mean +2 SD) Uncertainty in location/strength of trough, but mdt-stg Santa Ana likely

  42. 096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

  43. 096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Spaghetti: 500 mb Height (Single contour at 5760 m)

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

  45. 096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 500 mb Height and its Departure from Normal (# of SD)

  46. 096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: PMSL; 1000-500 mb Thickness; 10m Wind (mph)

  47. Very windy, very dry airmass 096h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble: Mean 2m RH (%) and its Standard Deviation

  48. ...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.

  49. Day -3 (Friday Oct, 19 2007) SREF Ensemble 21Z 18 October 2007 (Forecast hour = 75) AP Photo/Rick Bowmer AP Photo/Kevork Djansezian A back fire on a hillside in Jamul, California Key Points: Shift focus to the Short Range Ensemble Forecast (SREF) Begin to examine mesoscale details and diagnostics

  50. SREF Products Available on the SPC Website http://www.spc.noaa.gov/exper/sref/

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