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Ensemble Usage at the SPC: Current Status and Future Plans

Ensemble Usage at the SPC: Current Status and Future Plans . David Bright NOAA/NWS/NCEP/Storm Prediction Center Norman, OK NCEP 3 rd Ensemble User Workshop 31 October 2006. Where Americas Climate and Weather Services Begin. STORM PREDICTION CENTER. HAZARDOUS PHENOMENA.

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Ensemble Usage at the SPC: Current Status and Future Plans

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  1. Ensemble Usage at the SPC:Current Status and Future Plans David Bright NOAA/NWS/NCEP/Storm Prediction Center Norman, OK NCEP 3rd Ensemble User Workshop 31 October 2006 Where Americas Climate and Weather Services Begin

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

  3. SPC Forecast Products • TORNADO & SEVERE THUNDERSTORM WATCHES • WATCH STATUS MESSAGE • CONVECTIVE OUTLOOK • Day 1; Day 2; Day 3; Days 4-8 • MESOSCALE DISCUSSION • Severe Thunderstorm Potential/Outlook Upgrade • Thunderstorms not expected to become severe • Hazardous Winter Weather • Heavy Rainfall • FIRE WEATHER OUTLOOK • Day 1; Day 2; Days 3-8 • OPERATIONAL FORECASTS ARE BOTH DETERMINISTIC AND PROBABILISTIC Approximate Growth Exp to 8 days 75% of all SPC products are valid for < 24h period

  4. SPC Approach to Ensembles • Develop specialized guidance based on the particular hazardous weather application (severe wx, fire wx, winter wx) • Design guidance to… • Support SPC’s probabilistic forecast products • Help blend deterministic and ensemble methods • Use larger-scale environmental information to produce (downscaled) probabilistic guidance • Provide decision support for high impact weather • Properly gauge confidence • Alert for rare but significant events

  5. CONVECTIVE OUTLOOKSCategorical and Probabilistic Fcsts: Operational through Day 3; Exp through Day 8 Categorical Tornado (Hatched area 10% > F2) Wind Hail (Hatched area 10% > 2”)

  6. OPERATIONAL WATCH PROBABILITIES Severe Thunderstorm Watch 688 Probability Table

  7. Experimental Enhanced Thunderstorms OutlooksTwo periods (Division at 03Z; 10%, 40%, and 70% intervals) Probabilistic Probabilistic Thunderstorm Graphic valid until 3Z Thunderstorm Graphic valid 3Z to 12Z

  8. General EnsembleGuidance Used Operationallyat the SPC(SREF and MREF)

  9. Ensemble Mean MREF 500 mb: Mean Height Mean Temp Mean Wind GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006

  10. Ensemble Mean + Spread MREF 500 mb: Mean Height SD Height GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006

  11. Ensemble Mean + Departure from Normal MREF 500 mb: Mean Height Number of SD from normal GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006 (e.g., Grumm and Hart 2001)

  12. Ensemble Mean + Normalized Variance (Predictability: RMOP also available) MREF 500 mb: Mean Height Normalized variance GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006

  13. Postage Stamps: 500 mb HGHT 14 members + CTRL GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006

  14. Postage Stamps: Fosberg Index(Fosberg Index is a measure of fire threat due to weather conditions alone based on T, RH, and wind speed) 14 members + CTRL High Fosberg Index in a few members GFS Ensemble at SPC: F216 valid 00 UTC 21 June 2006

  15. Joint Probability (SREF)P(P12I < .01”) x P(V > 20 mph) x P(RH < 15%) x P(T > 60F) Explore the parameter space supporting critical fire weather conditions SREF Surface: Joint Probability Short-Range Ensemble at SPC: F027 valid 00 UTC 13 June 2006

  16. Joint Probability (SREF)P(MLCAPE > 1000 J/kg) x P(MLCL < 1 km) x P(0-1 SRH > 100 m^2/s^2) x P(0-6 km Shear > 40 kts) x P(C03I > .01”) First “Day 2” High Risk Severe Outlook ever issued by the SPC Explore the parameter space supporting strong or violent tornadoes [ > F2; Thompson et al. (2003) ] First “Day 2” High Risk Outlook Issued by the SPC 36h SREF Forecast Valid: 21 UTC 7 April 2006 SigTor Combination and Mean PMSL, 10m Wind Vectors

  17. Commonly Used Ensemble Statistics & Products at the SPC • Mean, Median, Max, Min, Spread, Range, Exceedance Probabilities, Joint and Combined Probabilities • Basic Weather Parameters (Temperature, Height, Wind, RH, etc.) • Derived Weather Parameters (for Severe, Winter, and Fire Weather, e.g., CAPE, Fosberg, SigTor, etc.)

  18. Calibrated EnsembleGuidance Used Operationallyat the SPC(Mostly SREF)

  19. Calibrated Guidance Productsat the SPC • Use the larger-scale environmental forecasts to produce calibrated ensemble guidance specific to hazards of importance to the SPC • Probability of Thunderstorms • Probability of Severe Thunderstorms • Probability of Snowfall Accumulation (HPC/SPC collaboration)

  20. Probability of Thunderstorms • Calibration largely based on two parameters • Probability (CPTP > 1) and Probability (P03I > .01”) • Frequentist approach over the previous year • Computationally fast and adaptable; updated weekly • Distance wgting accounts for regionalization • More details in Bright et al. (2005) available on SPC website • Output at 3h, 12h, and 24h periods (F03 – F87)

  21. Joint Probability (Assumed Independence) P(CPTP > 1) x P(Precip > .01”) 3 hr valid period: 21 UTC 31 Aug to 00 UTC 01 Sept 2004 15h Forecast Ending: 00 UTC 01 Sept 2004 Uncalibrated probability: Solid/Filled

  22. Uncalibrated Reliability: Joint Probability (5 Aug to 5 Nov 2004) Frequency [0%, 5%, …, 100%] Perfect Forecast No Skill Climatology P(CPTP > 1) x P(P03I > .01”)

  23. Calibrated Ensemble Thunder Probability 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

  24. Calibrated Ensemble Thunder Probability 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 +)

  25. Calibrated Reliability (5 Aug to 5 Nov 2004) Frequency [0%, 5%, …, 100%] Perfect Forecast Perfect Forecast No Skill Climatology No Skill Calibrated Thunder Probability

  26. Probability of Severe Thunderstorms • Calibration uses an ingredients based approach • CAPE/SHEAR [Organized updrafts] • CAPE/DCAPE [Downdraft potential] • CAPE/500 mb Temps [“Cold core” lows] • Calibrated thunderstorm guidance • Frequentist approach over previous year • Computationally fast and adaptable; updated weekly • More details in Bright et al. (2006) available on SPC website • Output at 3h, 12h, and 24h periods (F03 – F87)

  27. 24h Probability of a Severe Thunderstorm Shading begins at 15% SREF 24h calibrated probability of a severe thunderstorm F027 Valid 12 UTC 11 May 2005 to 12 UTC 12 May 2005

  28. SVR WX ACTIVITY 12Z 11 May 2005 to 12Z 12 May, 2005 a= Hail; w=Wind; t=Tornado SREF 24h calibrated probability of a severe thunderstorm F027 Valid 12 UTC 11 May 2005 to 12 UTC 12 May 2005

  29. Severe Verification Hail > .75” Wind > 50 kts Tornado 21 UTC F039 24h forecasts from 15 April to 15 October 2005 ROC Area= .86 Ave Hit = 15% Ave Miss= 3% (24h Fcst: F39, 21Z only) 21 UTC SREF only

  30. Probability of Snow Accumulating on Roads (HPC) • Calibration uses P(P03I), P(PTYPE), and two derived parameters • Simple surface parameter, f(TPBL,Ts, Qnet rad flux) • Parameter to estimate whether 3” snow melts in 3h • Frequentist approach over previous two years • MADIS road-state data serve as truth • Output at 3h and 6h periods (F03 – F87) • Experimental!

  31. Example: Calibrated Accumulations30h forecast – NCEP SREF 3h Probability of Road Accumulation – Valid 15 UTC 21 March 2006 Average March probability of accumulation (2004-2005) is 20%

  32. Calibrated Reliability of New Snow on Roads All 3h forecasts (F03-F87) from 1 Oct 2005 - 30 April 2006  OBS FREQ (%) FORECAST (%) 

  33. Storm-Scale Modeling • Subject of the SPC/NSSL 2005 Spring Program: • 3 explicit WRF models allowed for the creation of a “Poor person’s ensemble” • WRF-ARW2 (2 km grid space; OU/CAPS) • WRF-ARW4 (4 km grid space; NCAR) • WRF-NMM (4.5 km grid space; NCEP/EMC) • Explicit convection allowing forecasts • Interested in resolved storm-scale structures • Initiation, Mode, Evolution, Decay

  34. WRF 2 to 4.5 km ForecastsValid: F02426 May 2005 2 km ARW 4 km ARW 4.5 km NMM

  35. 2 km ARW 4 km ARW 4.5 km NMM WRF 2 to 4.5 km ForecastsValid: F02426 May 2005 “Spaghetti” of automated supercell detection: circles indicate a supercell identified within 25 miles All three WRF models contribute information to the supercell forecast

  36. Storm-Scale EnsembleNOAA Hazadous Weather Testbed (HWT) in Norman, OK • 2007 Spring Experiment will continue 2005 work • ~15 April 2007 through ~15 June 2007 • 2008 and 2009 will incorporate WRF-NMM and various upgrades • Collaboration between SPC and NSSL • OU/CAPS (NWC) • NCEP partners: AWC, EMC, HPC • WFO Norman • 10 members, 4 km explicit convection allowing, mixed physics WRFs (eastern 2/3 CONUS) • 2 km high-resolution deterministic WRF to accompany ensemble • Emphasis on small-scale, high-impact hazardous weather (e.g., supercell/updraft strength, convective mode & coverage, QPF) • Prototype for future NCEP regional SREF system

  37. Summary • Ensembles used operationally as decision support tool for SPC’s hazardous weather product suite • Severe Weather; Fire Weather; Winter Weather • Ongoing efforts include • Continue to develop specialized calibration for high-impact events • Enhance ensemble guidance for severe and fire weather programs in the Day 3 through Day 8 range (NAEFS; MREF) • HWT/Spring Experiment (2007-2009): Short-range, high resolution, explicit convection allowing WRF ensembles (Collaborative effort within NCEP and WFO Norman)

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