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David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK

Storm Prediction Center Forecast and Guidance Information for High-Impact Hazardous Weather Support. David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK All Hazards Workshop 6-7 February 2008 Memphis, TN. Where Americas Climate and Weather Services Begin.

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David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK

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  1. Storm Prediction Center Forecast and Guidance Information for High-Impact Hazardous Weather Support David Bright NOAA/NWS/Storm Prediction Center Science Support Branch Norman, OK All Hazards Workshop 6-7 February 2008 Memphis, TN 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. Framework for uncertainty • Decision making in uncertain environments • Subjective • Precise descriptions (quantitative)

  5. Hazardous Weather Forecasting • The Challenge: High impact events often occur on temporal and spatial scales below the resolvable resolutions of most observing and forecasting systems • Key premise: We must use knowledge of the environment and non-resolved processes to determine the spectrum of possible hazardous weather, where and when it may occur, and how it may evolve over time

  6. Hazardous Weather Forecasting • Observational data and diagnostic tools • Key input for short-term prediction, i.e., “Nowcast” • But high-impact weather events typically occur on scales smaller than standard observational data • Environment not sampled sufficiently to resolve key fields (especially 4D distribution of water vapor) • Model forecasts • Supplement observational data in short term • Increasing importance beyond 6-12 hr • Typically do not resolve most severe phenomena • NWP errors are related to both analysis errors and numerics/physics errors • Recognize the inherent uncertainty and address it through probabilistic or confidence-based products

  7. The Evolution of the Forecast National Academy of Sciences report (2006): • “Uncertainty is … a fundamental characteristic of weather, seasonal climate, and hydrological prediction, and no forecast is complete without a description of its uncertainty.” • “As forecast skill has increased in recent years, forecasts have become an important component of everyday and hazardous-weather decision making for many segments of society and the U.S. economy.” • “The entire enterprise should take responsibility for providing products that effectively communicate forecast uncertainty information.” Source: “Completing the Forecast” http://www.nap.edu/catalog/11699.html NCEP Strategic Plan: “Improve the user’s decision-making capabilities by including levels of forecast uncertainty in products and services.”

  8. The Evolution of the Forecast: 2008 • 15 years experience now in ensemble prediction in the US • Steady progress in making ensemble guidance more useful and skillful (and available!) • Increasing penetration of ensemble guidance into generation of high-impact forecasts, e.g., severe-storm forecasts, winter and fire weather. • Many WFOs and National Centers beginning to issue probabilistic or uncertainty forecasts • The system is evolving the public and mass communication sources toward probabilistic thinking • Many NWS products still largely deterministic

  9. Forecast Needs Vary from User to User They would if they could, my friend! But considering uncertainty information makes deterministic forecasts better, and adds value for some decision makers. So what’s the deal with all this uncertainty? What can I do with a 10% chance of rain? Just tell me if it’s going to rain or not.

  10. Examples of Expressing Uncertainty Although not quantified, AFDs express forecast confidence and uncertainty

  11. Probabilistic Forecasting at the SPC • Severe Convective Weather • Outlooks • Watches

  12. Convective OutlooksCategorical Forecast Characterizes the overall threat through a single deterministic forecast

  13. CONVECTIVE OUTLOOKSCategorical and Probabilistic: Operational through Day 8 Tornado (Hatched area 10% > EF2) Wind Hail (Hatched area 10% > 2”) Probabilistic forecasts provides additional information on confidence Probability of severe event within 25 miles of a point

  14. Verification of Probabilistic OutlooksHail (Initial Day 1, 2006) Significant hail forecast (hatched area)

  15. Verification of Probabilistic OutlooksWind (Initial Day 1, 2006)

  16. Verification of Probabilistic OutlooksTornado (Initial Day 1, 2006) Significant tornado forecast (hatched area) You can effectively gauge the likelihood of significant tornadoes within each watch

  17. Severe Weather WatchesProbabilistic Table (All watches are not created equal) Use the probabilities to refine the specific threat within the watch and gauge forecaster confidence in the specific convective hazards

  18. Verification of Watch ProbabilitiesTwo or More Tornadoes (2006)

  19. Verification of Watch ProbabilitiesOne or More Significant Tornadoes (2006) > EF2 You can effectively gauge the likelihood of significant tornadoes within each watch

  20. Experimental Enhanced Thunderstorms Outlooks(Space and probabilistic decomposition of the General Thunderstorm Line) Thunderstorm Graphic valid until 3Z Thunderstorm Graphic valid 3Z to 12Z http://www.spc.noaa.gov/products/exper/enhtstm/

  21. Verification of Enhanced Outlooks(All Forecasts, Past 90 days ending 01 Feb 2008)

  22. Verification of Enhanced Outlooks(Example of a single forecast: Jan 30, 2008)

  23. Guidance Addressing Uncertainty • Deterministic models reveal one end state, while ensembles • Provide a range of possible forecast solutions, yielding information on forecast confidence and uncertainty (probabilities) • Ensemble systems supplement traditional (higher resolution) deterministic models • Ensemble systems aid in decision support • Particularly if guidance calibrated (i.e., correct for systematic model bias and deficiencies in spread)

  24. Severe Event of April 7, 2006 • First ever Day 2 outlook High Risk issued by SPC • More than 800 total severe reports • 3 killer tornadoes and 10 deaths • SREF severe weather fields aided forecaster confidence

  25. Click on the fhour to activate dSREF/dt capability

  26. SREF Probability of STP Ingredients: Time Trends 48 hr SREF Forecast Valid 21 UTC 7 April 2006 Prob (MLCAPE > 1000 Jkg-1) X Prob (6 km Shear > 40 kt) X Prob (0-1 km SRH > 100 m2s-2) X Prob (MLLCL < 1000 m) X Prob (3h conv. Pcpn > 0.01 in) Shaded Area Prob > 5% Max 40%

  27. SREF Probability of STP Ingredients: Time Trends 36 hr SREF Forecast Valid 21 UTC 7 April 2006 Prob (MLCAPE > 1000 Jkg-1) X Prob (6 km Shear > 40 kt) X Prob (0-1 km SRH > 100 m2s-2) X Prob (MLLCL < 1000 m) X Prob (3h conv. Pcpn > 0.01 in) Shaded Area Prob > 5% Max 50%

  28. SREF Probability of STP Ingredients: Time Trends 24 hr SREF Forecast Valid 21 UTC 7 April 2006 Prob (MLCAPE > 1000 Jkg-1) X Prob (6 km Shear > 40 kt) X Prob (0-1 km SRH > 100 m2s-2) X Prob (MLLCL < 1000 m) X Prob (3h conv. Pcpn > 0.01 in) Shaded Area Prob > 5% Max 50%

  29. SREF Probability of STP Ingredients: Time Trends 12 hr SREF Forecast Valid 21 UTC 7 April 2006 Prob (MLCAPE > 1000 Jkg-1) X Prob (6 km Shear > 40 kt) X Prob (0-1 km SRH > 100 m2s-2) X Prob (MLLCL < 1000 m) X Prob (3h conv. Pcpn > 0.01 in) Shaded Area Prob > 5% Max 50%

  30. Severe Event of April 7, 2006 • First ever Day 2 outlook High Risk issued by SPC • More than 800 total severe reports • 3 killer tornadoes and 10 deaths • SREF severe weather fields aided forecaster confidence

  31. Uncertainty Exists in Every Prediction

  32. 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

  33. Day -7 (Monday Oct, 15 2007) Ensemble 00Z 15 October 2007 (Forecast hour = 168) Harris Fire at midday on October 23, 2007 Key Points: Confidence in western ridging increases considerably Additional support for an high-amplitude / offshore flow pattern

  34. 168h Forecast Valid 00 UTC 22 Oct 2007 GEFS Ensemble Mean: 500 mb Height and Vorticity

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