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  • Operational Application of Ensembles at the SPC:Fire Weather Forecasting

    David BrightNOAA/NWS/Storm Prediction CenterNorman, OK

    Advanced Fire Weather Forecasters CourseFire Weather Virtual ConferenceApril 25, 2008Where Americas Climate and Weather Services Begin

  • Nine NWS National Centers

  • Hail, Wind, TornadoesExcessive rainfallFire weather Winter weatherSTORM PREDICTION CENTER HAZARDOUS PHENOMENA

  • SPC Fire Weather OutlooksTo 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 forecastsLow RHModerate / strong windsAntecedent conditions / drought (NFDRS)Critical area for dry thunderstorms implies widespread lightning with minimal rainfall

  • Outline

    Motivation for Ensemble Forecasting

    SPC Ensemble Applications in Fire WeatherMedium 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 WeatherMedium to Short-range Case Study (Southern California Fires Oct. 2007)

    Ensemble Calibration and Decision Support

    Summary and Future Directions

  • Example: A deterministic approach57h NAM Forecast valid 21 UTC 25 June 200710m Wind (> 15 mph); 2m RH (< 20%) (filled)

  • Example: A deterministic approachTruth: SPC OA valid 21 UTC 25 June 200710m Wind (> 15 mph); 2m RH (< 20%) (filled)

  • Example: A deterministic approach57h NAM Forecast Valid: 21 UTC 25 June 2007Verifying 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:

    ObservationsDensityErrorRepresentativeQCAnalysisModels LBCs, etc.SatelliteLandData and Models

  • Uncertainty in Initial AnalysesNCEP Eta Data Assimilation850 mb Initial Analysis (Hgt, Tmp, Wnd) 20 March 2006 12 UTCNCEP WRF Data Assimilation850 mb Initial Analysis (Hgt, Tmp, Wnd) 20 March 2006 12 UTCTwo state of the art assimilation systems, and two similar but clearly different analyses (even over land).

  • 500 mb Hgt RMSE Winter 2006-2007Slope of Ens Mean (solid) is less steepSkill is retained longerSame results in summerDeterministic models lose skill faster than ensemble mean Ens SpreadEns MeanGFS and Ens ControlClimatologyEns mean reduces RMSE after Day 3. Improvement increases with time and extends predictabilitySpread-skill suggests ensemble is underdispersiveError Growth with Time: GFS1.41 x Climate RMSE(Limit of Skill)Ensemble skill ~12-13 daysDeterministic skill ~10 days

  • Weather models...All forecasts contain errors that increase with timeDoubling time of small initial errors ~1 to 2 daysMaximum large-scale (synoptic to planetary) predictability ~10 to 14 daysEnsemble systemsA collection of models that provide information on the range of plausible forecasts and extend predictabilityIncreasing in popularityPrinciples scale (global high-res)Requires tools to view the large number of models using a slightly different approach (statistical)

    Weather forecasting: Its impossible to be deterministically correct all of the time!

  • ModelRes Levels Mems Cld PhysicsConvectionGFS 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: GEFSFour times per day: 00, 06, 12, 18 UTC

  • ModelRes Levels Mems Cld PhysicsConvectionGEM ~100 km 28 20 Sundqvist (mixed) MixedNorth American Ensemble Forecast System (NAEFS)ModelRes Levels Mems Cld PhysicsConvectionGFS T126* (~ 105 km) 28 20 GFS physics Simple A-SNAEFS 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 costshttp://www.weatheroffice.gc.ca/ensemble/index_naefs_e.htmlEnsembles 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 domainModel grid lengths 32-45 km Multi-model: Eta, RSM, WRF-NMM, WRF-ARWMulti-analysis: NAM, GFS initial and boundary conds.IC perturbations and physics diversityEnsembles Available at the SPC: SREF

  • Ensemble Guidance at the SPCDevelop specialized guidance for the specific application (severe weather, fire weather, winter weather)

    Design guidance thatHelps blend deterministic and ensemble approachesFacilitates transition toward probabilistic forecastsConsiderable diagnostic parameter evaluation in probability spaceAids in decision support of high impact weatherGauge confidence Alert for potentially significant events

  • Outline

    Motivation for Ensemble Forecasting

    SPC Ensemble Applications in Fire WeatherMedium to Short-range Case Study (Southern California Fires Oct. 2007) Focus on Sunday afternoon: 00Z 22 Oct 2007Ensemble Calibration and Decision Support

    Summary and Future Directions

  • 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 eventEnsemble 00Z 14 October 2007 (Forecast hour = 192)

  • GEFS Ensemble Mean: 500 mb Height and Vorticity192h 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

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

  • GEMGFSNCEPE015GEMEN009 Control Control http://www.weatheroffice.gc.ca/ensemble/cartes_e.html#NAEFS Postage Stamp (Subset!) 500 mb Height

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

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

  • 192h Forecast Valid 00 UTC 22 Oct 2007GEFS Ensemble: Mean 2m RH (%) and its Standard DeviationBreezy, 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 Ensemble 00Z 16 October 2007 (Forecast hour = 144)

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

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

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

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

  • 144h Forecast Valid 00 UTC 22 Oct 2007GEFS Ensemble: Mean 2m RH (%) and its Standard DeviationWindy, 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 Ensemble 00Z 17 October 2007 (Forecast hour = 120)

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

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

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

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

  • 120h Forecast Valid 00 UTC 22 Oct 2007GEFS Ensemble: Mean 2m RH (%) and its Standard DeviationWindy, ve

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