Applications of Ensemble Prediction - a Historical Perspective Steve Tracton Office of Naval Research Arlington, VA (Formally of NWS/NCEP)

KEY POINTS THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION SCREAMING MESSAGE: THERE WILL ALWAYS BE VARYING DEGREES OF UNCERTAINTIES IN FORECASTS (“Chaos Theory”)

KEY POINTS THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), OPERATIONAL First formal attention to the real possibility of OPERATIONAL Predictability ensemble prediction at ECMWF Workshop on Predictability In the Medium Range and Extended Range, 1986 GLOBAL EPS Ultimately led to operational GLOBAL EPS at ECMWF and NMC in Dec 1992 Followed from Sufficient CPU resources becoming available Scientific basis for generating “dynamically constrained” initial state perturbations (SVs, Breeding) Development of output products

ENSEMBLE FORECASTING Give Me Odds

KEY POINTS THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), THE OBJECTIVES BEING TO: ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), THE OBJECTIVES BEING TO: PROVIDE RELIABLE INFORMATION ON FORECAST UNCERTAINTIES FROM THE SPREAD (DIVERSITY) AMONGST ENSEMBLE MEMBERS NET RESULT - ENHANCE UTILITY/VALUE OF NWP FOR VIRTUALLY ALL APPLICATIONS USE TO: Ascertain most likely deterministic prediction Confidence in deterministic forecast Same, plus identifying relative likelihood of alternative scenarios maximum informationFull probability distribution – maximum information NOT NECESSARILY SKILL

NOGAPS ECMWFMRF UKMET Providing EPS = Acceptance and Use /

RUN TO RUN MODEL CONTINUITY GOOD BAD TODAY’S DAY 3YESTERDAY’S DAY 4 NEW 84 HR MRF OLD 108 HR MRF NEW 96 HR ECMWF OLD 120 HR ECMWF WHICH SOLUTION IS PREFERRED?  DETERMINISTIC THINKING

HPC’s Extended Forecast Discussion (released Mar 2, 2001, at 3:38 p.m.) EPS NOW CONSIDERED INDISPENSIBLE TO HPC MEDIUM RANGE FORECASTS (Jim Hoke) STEEP LEARNING CURVE FOR NEW PARADIGM:NO A- PRIORI BEST SINGLE OUTCOME “DETERMINISM IS DEAD” ?? NOT YET; BUT…

American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!) “ The AMS endorses probability forecasts and recommends their use be substantially increased.” “ Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along, through canceling a trip,to evacuation from an impending threat)

Schematic of how a probabilistic model forecast can be used for risk-based decision-making. P1, P2 … PN = predicted variables of interest, for example, precipitation amount Pcr = user-specified “critical value” of P which, if exceeded, requires an action or decision T = chance of critical value being exceeded Tcr = user-specified tolerance level (depending on societal, monetary, and/or environmental considerations). P1 P2 P3 P4. P N Model F(P) Compare T with Tcr Take appropriate action Pcr T P

American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!) “ The AMS endorses probability forecasts and recommends their use be substantially increased.” “ Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along, through canceling a trip, to evacuation from an impending threat) necessary, “ Probability Forecasts are particularly useful, even necessary, to reliably provide early warnings of extreme weather events” TO AVOID, E.G.

Not Good- especially when effecting DC (just after announce- ment of new Super Computer by NWSHQ MAJOR SNOWSTORM AMBUSHES WASHINGTON

FOR FORECASTERS, ANOTHER …

American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!) “ The AMS endorses probability forecasts and recommends their use be substantially increased.” “ Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along through canceling a trip to evacuation from an impending threat) Requires: Conveying rationale and nature of uncertainties Products/graphics/presentations that are readily comprehensible and relevant

KEY POINTS THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION ENSEMBLE PREDICTION - REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”) - CONSISTS OF MULTIPLE PREDICTIONS FROM SLIGHTLY DIFFERENT INITIAL CONDITIONS AND/OR WITH VARIOUS VERSIONS OF MODELS, THE OBJECTIVES BEING TO: REALIZING THE PRACTICAL UTILITY/VALUE OF ENSEMBLES ACCOMPLISHED VIA A VARIETY OF PRODUCTS DESIGNED TO CONDENSE AND MAXIMIZE INFORMATION CONTENT FOR USERS REALIZING THE PRACTICAL UTILITY/VALUE OF ENSEMBLES ACCOMPLISHED VIA A VARIETY OF PRODUCTS DESIGNED TO CONDENSE AND MAXIMIZE INFORMATION CONTENT FOR USERS Products/graphics/presentations must be readily comprehensible and relevant and relevant (MUST BE USER SPECIFIC AND USER FRIENDLY)  USER FEEDBACK ESSENTIAL

Products: Stamp maps

TYPES OF PRODUCTS Roots of EPS products largely provided by Ed Epstein with graphical depictions to illustrate how uncertainty information could enhance forecast value (1971); formal But, no further formal consideration of post processing and presenting EPS output until 1992 ECMWF Workshop on New Developments in Predictability (List of recommended generic products largely reflected “concept demonstration” mode of EPS experiments at NMC/CAC, Tracton and Kalnay, 1993) SPAGHETTI CHARTS  SPAGHETTI CHARTS: now one of the most recognizable and symbolic products of EPS

TYPES OF PRODUCTS SPAGHETTI CHARTS MEAN/SPREAD PROBABILITIES STORM TRACKS CLUSTERS VERTICAL PROFILES METEOGRAMS ENSEMBLE DERIVED MOS

010519/0000V63 SREFX-CMB; LIFTED INDEX PROB 0F < -4

5-Day ECMWF Ensemble Prediction of Typhoon Rusa

TYPES OF PRODUCTS SPAGHETTI CHARTS MEAN/SPREAD PROBABILITIES STORM TRACKS CLUSTERS VERTICAL PROFILES METEOGRAMS ENSEMBLE DERIVED MOS CAN BE APPLIED TO VIRTUALLY ALL MODEL AND MODEL DERIVED PARAMETERS AND MODEL OUTPUT DRIVERS OF SECONDARY SYSTEMS, E.G., WAVE, HYDROLOGICAL,POLUTION DISPERSION MODELS ULTIMATELY CAN (MUST) BE PROPOGATED TO USER SPECIFCIC QUANTITIES, E.G., UMBRELLA SALES, ENERGY USEAGE, TYPE OF “SMART” MUNITIONS, ETC., ETC., ETC., ETC., ETC., ETC OF “SMART” MUNITIONS, ETC., ETC., ETC., ETC., ETC., ETC ….

MANY NEW AND VARIED PRODUCTS POSSIBLE; BUT, MOST SIGNIFICANT ADVANCE OVER PAST YEARS HAS BEEN EXPONENTIAL GROWTH IN GRAPHICS CAPABILITIES - ANIMATION, ZOOMING, 3-D, ETC. - AND PROLIFERATION OF PCs AND HIGH SPEED INTERNET

MANY NEW AND VARIED PRODUCTS POSSIBLE; BUT, MOST SIGNIFICANT ADVANCE OVER PAST YEARS HAS BEEN EXPONENTIAL GROWTH IN GRAPHICS CAPABILITIES - ANIMATION, ZOOMING, 3-D, ETC. - AND PROLIFERATION OF PCs AND HIGH SPEED INTERNET SO, REAL CHALLENGE IS MORE FULLY EXPLOITING POTENTIAL VALUE OF EPS IN BOTH PUBLIC AND PRIVATE SECTORS

CONVEYING UNCERTAINTY TO PUBLIC VIA MEDIA - A CRITICAL LINK (see IABM.org) Bob Ryan

MON TUES WED THURS FRI % THIS

INCONSISTENT WITH PREDICTABILITY LIMITS NOT THIS

Visualizing Uncertainty in Mesoscale Meteorology APL Verification Methodology 21 May 2002 Scott Sandgathe

Questions ??

SPAGHETTI CHART

What a mess!!

END

BACKUP SLIDES

EVEN EXPERTS CAN HAVE A BAD DAY

One model (even with forecaster input) is an all or nothing proposition => “ One detailed mesoscale model based forecast could allow the user to make highly specific and detailed inaccurate forecasts.” (after Grumm) High Resolution Mesoscale models – allow us to see features not in coarser models – But: even small timing and placement errors can be significant in attempt to accurately forecast details (see Mass, et al., 3/02 BAMS!!!). – But But: Forcaster judgement could mitigate

Why we need ensembles – Deal with uncertainties in analyses and model formulation – But: Requires tradeoffs when computer resources limited (e.g., model resolution) – But But: Mesoscale predictability often substantially controlled by synoptic predictability (and uncertainties therein) => Subjective or statistically based downscaling possible to get uncertainties in mesoscale weather Ideal: Ensembles with highest resolution justifiable Compromise: Combination of single (or few) high resolution and coarser resolved ensemble

ADDITIONAL WEB SITES WITH ENSEMBLE PRODUCTS AND INFORMATION Univ of Utah: model_ens.html FNMOC: Canada: index.html CDC: ens.html State College:

ENSEMBLE FORECASTING Give Me Odds

EVEN EXPERTS CAN HAVE A BAD DAY

YOUR FORECAST HAS A 30% CHANCE OF BEING 70% CORRECT CHANCE OF BEING 70% CORRECT

Uncertain location of incoming western trough From CDC web site: Uncertain amplitude of eastern trough 3-day forecast from 00 UTC 11/2/01, spaghetti diagram for ensemble global

SOME NCEP ENSEMBLE MEMBERS OFFER A MORE “DIGGY” CENTRAL U.S. TROF THAN THE OPERATIONAL MRF..BUT NOT AS STRONG AS THE ECMWF “SPAGHETTI” DIAGRAM DAY3 564 DM CONTOUR NCEP ENSEMBLE