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Applications of Ensemble Predict

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					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”),

First formal attention to the real possibility of OPERATIONAL
ensemble prediction at ECMWF Workshop on Predictability
In the Medium Range and Extended Range, 1986

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
Give Me Odds




         ENSEMBLE   FORECASTING
                             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:


        PROVIDE RELIABLE INFORMATION ON FORECAST
    UNCERTAINTIES FROM THE SPREAD (DIVERSITY) AMONGST
                    ENSEMBLE MEMBERS

  USE TO:
• Ascertain most likely deterministic prediction
• Confidence in deterministic forecast
• Same, plus identifying relative likelihood of alternative scenarios
• Full probability distribution – maximum information
        NET RESULT - ENHANCE UTILITY/VALUE OF NWP FOR
                      NOT NECESSARILY SKILL
                  VIRTUALLY ALL APPLICATIONS
              /
Providing EPS = Acceptance and Use




  MRF                 ECMWF




 NOGAPS               UKMET
 WHICH RUN MODEL CONTINUITY
 RUN TO SOLUTION IS PREFERRED?
    DETERMINISTIC THINKING
  TODAY’S DAY 3          YESTERDAY’S DAY 4


                  GOOD

NEW 84                   OLD 108
HR MRF                   HR MRF




                   BAD


NEW 96 HR                OLD 120
ECMWF                    HR ECMWF
         HPC’s Extended Forecast Discussion
         (released Mar 2, 2001, INDISPENSIBLE TO
    EPS NOW CONSIDEREDat 3:38 p.m.)
 HPC MEDIUM RANGE FORECASTS (Jim Hoke)
EXTENDED FORECAST DISCUSSION FOR 05 THRU 09 MAR 2001
HYDROMETEOROLOGICAL PREDICTION CENTER...NCEP...NWS...WASHINGTON DC
3:38 PM EST FRI MAR 02 2001...FINAL VERSION.

POTENTIALLY SERIOUS E COAST STORM STARTING LATE ON DAY 3 (SUN).

THREAT OF HEAVY SNOW AND STRONG COASTAL WINDS CONTINUES FOR THE MID-ATLANTIC..

...MODEL OVERVIEW AND DISCUSSION...

WE NOW HAVE HIGHER CERTAINTY THAT THERE WILL INDEED BE THE DEVELOPMENT OF A MAJOR STORM ALONG THE EAST COAST...MAYBE
EVEN A BLIZZARD...IN THE DAY 2-3 PERIOD.

THE VERY STRONG BLOCK NW OVER THE SOUTHERN DAVIS STRAIT WILL DRIFT WESTWARD AND WEAKEN SLOWLY OVER THE NEXT DAYS...BUT
CONTROL THE WEATHER OVER NOAM THE ENTIRE TIME.

CONCERNING THE EAST COAST CYCLOGENESIS...MODELS ARE GROUPED INTO THREE SCHOOLS OF THOUGHT. THE ECMWF HAS NOW JOINED THE
AVN/MRF NOGAPS IN FORECASTING STRONG CYCLOGENESIS EAST OF CAP HATTERAS IN THE 60-72 HOUR PERIOD...POSSIBLY EVEN A
SNOWSTORM OF HISTORICAL PROPORTIONS FOR THE MID ATLANTIC STATES AND SOUTHERN NEW ENGLAND.

THE MIDDLE SCHOOL IS PORTRAYED BY THE CANADIAN WHICH DROPS A COLD VORTEX SOUTHWARD ACROSS WV INTO NC DAYS 3-4. WHILE IT

                                                          STEEP LEARNING CURVE
                                                       “DETERMINISM IS DEAD” ??
STILL HAS ITS MAIN SURFACE STORM FAR OUT AT SEA...IT IS SOMEWHAT SIMILAR AT 500 MILLIBARS TO THE LATEST AVN RUN THAT DOES
INDEED SHOW AN INTENSIFYING STORM.
                                                       FOR NEW PARADIGM:NO A-
LAST NIGHTS UKMET AND MODEL ENSEMBLE DATA ARE IN THE MORE CONSERVATIVE SCHOOL. THEY ARE CONSISTENT IN SLOWLY MOVING A
                                                    PRIORI BEST YET; BUT… THE SERN STATES
                                                                  NOT SYS MOVING ACROSS
DEEP COLD VORTEX ACROSS THE ERN LAKES DAY 3. THEIR SOLUTIONS SUPPRESS STRONGSINGLE OUTCOME FAR ENOUGH
SOUTH THAT HEAVY PCPN DOES NOT GET INTO NYC AND NEW ENG SUN-TUE. UNTIL TODAY...THE CANADIAN MODEL WAS MORE LIKE THE
NOGAPS.
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
                   P1
                                           probabilistic model forecast
                                           can be used for risk-based
                   P2                      decision-making.


                   P3       F(P)
                                          Pcr                Compare T
 Model                                                       with Tcr
                   P4
                   .                                T
                   .                                         Take
                   PN                                        appropriate
                                                              action
                                           P

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).
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, to reliably provide early warnings of extreme
weather events”
TO AVOID, E.G.
MAJOR SNOWSTORM AMBUSHES WASHINGTON


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

    Products/graphics/presentations must be readily comprehensible
     and relevant
         (MUST BE USER SPECIFIC AND USER FRIENDLY)

                               
               USER FEEDBACK ESSENTIAL
Cntr T255                            Cluster 1                  OPER T511                       Cluster 1                                  Verifying Analysis

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                                                                                                                                                                                                                                                                                                    H
 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);

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: 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 ….
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


                        40%

     36    28      23         21    31
40


30


20


10              THIS
INCONSISTENT WITH PREDICTABILITY LIMITS




   NOT THIS
Visualizing Uncertainty
           in
Mesoscale Meteorology



     APL Verification Methodology
            21 May 2002
          Scott Sandgathe
SPAGHETTI CHART
What a mess!!
END
BACKUP SLIDES
EVEN EXPERTS CAN HAVE A BAD DAY
•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

•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)
• 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
Give Me Odds




         ENSEMBLE   FORECASTING
EVEN EXPERTS CAN HAVE A BAD DAY
 YOUR FORECAST HAS A 30%
CHANCE OF BEING 70% CORRECT
3-day forecast from 00 UTC 11/2/01, spaghetti diagram for ensemble
global
  Uncertain location of
incoming western trough

                                            Uncertain amplitude
                                            of eastern trough




From CDC web site:
http://www.cdc.noaa.gov/map/images/ens/ens.html
      “SPAGHETTI” DIAGRAM
                   564 DM CONTOUR
                   NCEP ENSEMBLE
   SOME NCEP
   ENSEMBLE
MEMBERS OFFER
A MORE “DIGGY”
  CENTRAL U.S.
TROF THAN THE
 OPERATIONAL
MRF..BUT NOT AS
STRONG AS THE
     ECMWF
                      DAY3

				
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posted:10/26/2010
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