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Applications of Ensemble Applications of Ensemble Prediction - a Historical Prediction - a Historical
PerspectivePerspective
Steve Tracton Office of Naval Research
Arlington, VA
(Formally of NWS/NCEP)
KEY POINTSKEY 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 POINTSKEY POINTS• THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN
INITIAL CONDITIONS AND MODEL FORMULATION
• ENSEMBLE PREDICTIONENSEMBLE PREDICTION – FROM EARLY 90’S ON, – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), NWP (“WAVE OF THE FUTURE”),
First formal attention to the real possibility of OPERATIONALOPERATIONALensemble prediction at ECMWF Workshop on PredictabilityPredictabilityIn the Medium Range and Extended Range, 1986
Ultimately led to operational GLOBALGLOBAL EPS 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 POINTSKEY POINTS• THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN
INITIAL CONDITIONS AND MODEL FORMULATION
• ENSEMBLE PREDICTIONENSEMBLE PREDICTION – FROM EARLY 90’S ON, – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), NWP (“WAVE OF THE FUTURE”), THE OBJECTIVES BEING THE OBJECTIVES BEING TOTO::
PROVIDE RELIABLE INFORMATION ON FORECAST PROVIDE RELIABLE INFORMATION ON FORECAST UNCERTAINTIES FROM THE SPREAD (DIVERSITY) AMONGST UNCERTAINTIES FROM THE SPREAD (DIVERSITY) AMONGST
ENSEMBLE MEMBERSENSEMBLE MEMBERS
NET RESULTNET RESULT - ENHANCE UTILITY/VALUE OF NWP FOR - ENHANCE UTILITY/VALUE OF NWP FOR VIRTUALLY ALL APPLICATIONSVIRTUALLY ALL APPLICATIONS
USE TO:USE TO:• Ascertain most likely deterministic prediction• Confidence in deterministic forecast• Same, plus identifying relative likelihood of alternative
scenarios
• Full probability distribution – maximum informationmaximum informationNOT NECESSARILY SKILL
NOGAPS
ECMWFMRF
UKMET
Providing EPS = Acceptance and Use /
RUN TO RUN MODEL CONTINUITY
GOOD
BAD
TODAY’S DAY 3 YESTERDAY’S DAY 4
NEW 84 HR MRF
OLD 108HR MRF
NEW 96 HRECMWF
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 CURVEFOR 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..PN
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)
“Probability Forecasts are particularly useful, even necessary,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 …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: Requires:
Conveying rationale and nature of uncertainties Conveying rationale and nature of uncertainties
Products/graphics/presentations that are readily Products/graphics/presentations that are readily comprehensible and relevantcomprehensible and relevant
KEY POINTSKEY 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 REALIZING THE PRACTICAL UTILITY/VALUE OF ENSEMBLES ACCOMPLISHED VIA A VARIETY OF PRODUCTS DESIGNED ACCOMPLISHED VIA A VARIETY OF PRODUCTS DESIGNED TO CONDENSE AND MAXIMIZE INFORMATION CONTENT FOR TO CONDENSE AND MAXIMIZE INFORMATION CONTENT FOR USERSUSERS
Products/graphics/presentations must be readily comprehensible Products/graphics/presentations must be readily comprehensible and relevantand relevant
(MUST BE USER SPECIFIC AND USER FRIENDLY)
USER FEEDBACK USER FEEDBACK ESSENTIALESSENTIAL
Products: Stamp maps
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Verifying Analysis
MSLP (countour every 5hPa) and Temperature at 850hPa (only-6 and 16 isolines are plotted)Monday 26 May 2003 12UTC ECMWF Forecast t+168 VT: Monday 2 June 2003 12UTC Surface: mean sea level pressureECMWF ENSEMBLE FORECASTS
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TYPES OF PRODUCTSTYPES OF PRODUCTS Roots of EPS products largely provided by Ed Epstein with graphical depictions to illustrate how uncertainty information could enhance forecast value (1971);
But, no further formalformal 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 CHARTSSPAGHETTI CHARTS: now one of the most recognizable and symbolic products of EPS
TYPES OF PRODUCTSTYPES 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 PRODUCTSTYPES 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 CAN BE APPLIED TO VIRTUALLY ALL MODEL AND MODEL DERIVED PARAMETERS AND MODEL OUTPUT DRIVERS OF SECONDARY PARAMETERS AND MODEL OUTPUT DRIVERS OF SECONDARY
SYSTEMS, E.G., WAVE, HYDROLOGICAL,POLUTION DISPERSION SYSTEMS, E.G., WAVE, HYDROLOGICAL,POLUTION DISPERSION MODELSMODELS
ULTIMATELY CAN (MUST) BE PROPOGATED TO USER ULTIMATELY CAN (MUST) BE PROPOGATED TO USER SPECIFCIC SPECIFCIC QUANTITIES, E.G., UMBRELLA SALES, ENERGY USEAGE, TYPEQUANTITIES, E.G., UMBRELLA SALES, ENERGY USEAGE, TYPEOF “SMART” MUNITIONS, ETC., ETC., ETC., ETC., ETC., ETCOF “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 SO, REAL CHALLENGE IS MORE FULLY EXPLOITING POTENTIAL VALUE OF EPS IN EXPLOITING POTENTIAL VALUE OF EPS IN BOTH PUBLIC AND PRIVATE SECTORSBOTH PUBLIC AND PRIVATE SECTORS
CONVEYING UNCERTAINTY TO PUBLIC VIA MEDIA - A CONVEYING UNCERTAINTY TO PUBLIC VIA MEDIA - A CRITICAL LINK (see IABM.org) CRITICAL LINK (see IABM.org)
Bob Ryan
MON TUES WED THURS FRI
10
20
30
4036 28 23 21 31
40%
THIS
INCONSISTENT WITH PREDICTABILITY LIMITS
NOT THIS
Visualizing Uncertaintyin
Mesoscale Meteorology
APL Verification Methodology21 May 2002
Scott Sandgathe
Questions ??
SPAGHETTI CHARTSPAGHETTI 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:http://www.met.utah.edu/jhorel/html/models/model_ens.html
FNMOC:http://152.80.49.204/PUBLIC/
Canada:http://www.cmc.ec.gc.ca/rpn/ensemble_products/index.html
CDC:http://www.cdc.noaa.gov/~map/maproom/ENS/ens.html
State College:http://bookend.met.psu.edu/ensembles/Ensemble.html
ENSEMBLE FORECASTING
Give Me Odds
EVEN EXPERTS CAN HAVE A BAD DAY
YOUR FORECAST HAS A 30% YOUR FORECAST HAS A 30% CHANCE OF BEING 70% CORRECTCHANCE OF BEING 70% CORRECT
Uncertain location of incoming western trough
From CDC web site: http://www.cdc.noaa.gov/map/images/ens/ens.html
Uncertain amplitudeof eastern trough
3-day forecast from 00 UTC 11/2/01, spaghetti diagram for ensembleglobal
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