probabilistic hydrometeorological forecasts hydromet 00-3 thursday, 11 may 2000 bill drzal noaa/nws...
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Probabilistic Hydrometeorological
Forecasts
Hydromet 00-3Thursday, 11 May 2000
Bill Drzal
NOAA/NWS Pittsburgh, PA
OVERVIEW
• Probabilistic Hydrometeorological System
• PQPF Methodology
• Interactive PQPF Software
• Probabilistic Reasoning
• PQPF Case Study
• Probabilistic River Stage Forecast
• River Forecast Interface
NWS End-to-End Probabilistic Risk Reduction
• Define AWIPS-compatible PQPF/PRSF methodologies, PQPF guidance, and public product formats.
• Approach is grid-based and benefits from HPC, TDL and OH input.
• 1998-2000. With funding, similar Risk Reductions in other Regions after 2001.
• UVA/PBZ/RLX/OHRFC/TDL/HPC/OH/ OM• Users (County EMA & Barge Industry)
PROBABILISTIC HYDROMETEOROLOGICAL
FORECASTING SYSTEM
ProbabilisticProbabilistic QuantitativeQuantitative PrecipitationPrecipitation
Forecasting SystemForecasting SystemPQPFPQPF
WFO
To improve the reliability and lead time of flood warnings.To improve the reliability and lead time of flood warnings.
Probabilistic River StageProbabilistic River Stage Forecasting SystemForecasting System
PRSFPRSF
River FloodRiver FloodWarning SystemWarning System
RFIRFI
USERSUSERS
RFC
WFO
Probabilistic RSFs
Flood Watches & Warnings
FORECASTFORECASTMETHODOLOGYMETHODOLOGY
LOCALLOCALCLIMATICCLIMATIC
DATADATA
FORECAST FORECAST VERIFICATIONVERIFICATION
THE PQPF SYSTEM
WFOWFO
RFCRFC
GUIDANCEGUIDANCE
PQPF METHODOLOGY
PQPFTOTAL AMOUNT
• Precipitation amount accumulated during a period: W
• Probability of Precipitation: PoP=P(W>0)
• Conditional Exceedance Fractiles of Amount:– P(W>X25|W>0)=0.25
– P(W>X50|W>0)=0.50
CONDITIONAL EXCEEDANCE FUNCTIONW = 24-hour Basin Average Precipitation Amount
0
0.25
0.5
0.75
1
50% CREDIBLE INTERVAL
ww
(P W>w|W>0)(P W>w|W>0)
X75 - 75% FractileX50 - 50% FractileX25 - 25% Fractile
Conditional Probability
X75 X50 X25
calculated
ASSESSMENT OF CONDITIONAL EXCEEDANCE FRACTILES
X50
Judgments of equally likely events
X25
ACTUAL PRECIPITATION W
HYPOTHESIS: X50 <WACTUAL PRECIPITATION W
P(W>X25 |W >0)=.25
P(W>X50 |W>0)=.50
HYPOTHESIS: 0<W
PQPFTemporal Disaggregation
• Precipitation amount during subperiod i: Wi
• Expected subamounts: mi=E(Wi|W>0); i=1,2,3,4;12,34
• Expected fractions: zi=E(Wi/W|W>0); i=1,2,3,4;12,34
13%
17%57%
13% z1z2Z3Z4
A PQPF is Never Right or Wrong
It Just Needs to be
Well Calibrated!
INTERACTIVE SOFTWARE FOR PROBABILISTIC
QUANTITATIVE PRECIPITATION FORECASTING
Purpose
• Aids field forecasters in preparing PQPFs.
• Provides crucial input to Probabilistic River Stage Forecast System.
• Prototype Testing– Weather Service Forecast Offices
• Pittsburgh, PA
• Charleston, WV
PROBABILISTIC REASONING
SCHEME FOR JUDGMENTAL PROCESSING OF
INFORMATION INTO PQPF
NMC NUMERICAL
MODELS
TDL MODEL OUTPUT STATISTICSNMC MANUAL GUIDANCE
LOCALSUBJECTIVE
ANALYSIS
REVIEW-MODEL ASSESSMENT/COMPARISON
-GUIDANCE REVIEW
ISPRECIP
PROBABLE?
STOP
ISSIGNIFICANT
AMOUNTPROBABLE?
FURTHUR ANALYSIS-MODEL OUTPUTS-LOCAL ANALYSIS
WHAT IS PREDICTABILITY OF
PATTERN?
WHAT ISPREDICTABILITY OF
PATTERN
LIMITEDFURTHER ANALYSIS
-FOLLOW CLOSELYLOCAL ADJUSTMENTS
TO GUIDANCE-LARGE UNCERTAINTY
-FOLLOW CLOSELYGUIDANCE WITH MINORLOCAL ADJUSTMENTS
-SMALLER UNCERTAINTY
-MIX GUIDANCE WITH LOCAL
ADJUSTMENTS-LARGER UNCERTAINTY
-FOLLOW GUIDANCECLOSELY
-SMALLERUNCERTAINTY
LOCAL CLIMATOLOGICALGUIDANCE
INTEGRATIONEXPERT KNOWLEDGE OF
LOCAL HYDROMETINFLUENCES
OBSERVATIONS
NO
YES
YES NO
LOW
HIGH
LOW HIGH
WORKING QPF
POSTERIOR QPF
RE
VIE
WD
EV
EL
OPM
EN
TA
DJU
ST
ME
NT
INT
EG
RA
TIO
N
MAKING A PQPF
DEVELOPMENDEVELOPMENTT
REVIEWREVIEW
ADJUSTMENADJUSTMENTT
INTEGRATIONINTEGRATION
THE REVIEW PHASEExamine Observations and Guidance
• Review Initial Conditions– Diagnose past/current conditions, trends
and how well models initialized.
– Compare Model Outputs• If Agree…confidence is increased.• If Not…uncertainty decreases confidence.
THE DEVELOPMENT PHASEJudge Likelihood/Predictability of
Precipitation• Ask three questions:
– Is precipitation probable?– Is a significant amount probable?– What is predictability of pattern?
• No significant amount & predictability:– high…more confidence in guidance.– low…less confidence/further analysis
• Significant amount…further analysis.
THE ADJUSTMENT PHASEAdjust Guidance/Ascertain Uncertainty • Nonsignificant Event
– Predictability high…follow guidance/uncertainty smaller.– Predictability low…may adjust guidance/ uncertainty larger.
• Significant Event– Predictability high…local analysis should corroborate
guidance/uncertainty smaller.– Predictability low…extensive use of analysis, may
significantly adjust guidance/uncertainty larger.
• “Working PQPF”…includes amounts & uncertainties.
THE INTEGRATION PHASE“Working PQPF” Integrated with LCG
• Integrate Information From:– “Working PQPF”– Knowledge of local influences– Local Climatic Guidance (LCG)
• Uncertainty small…tend toward “Working PQPF”
• Uncertainty large…tend toward LCG
PQPF CASE STUDYWell Organized Frontal System
May18-19,1999
THE REVIEW PHASECase Study May 18-19, 1999
• Examine Observations and Guidance– 00Z 5/18/99 ETA Model
• Models initialized well & in agreement
–confidence increased
THE DEVELOPMENT PHASE Case Study May 18-19, 1999
• Judge Likelihood/Predictability of Precipitation– A significant amount of precipitation probable– Predictability of pattern is high
• Models in agreement on speed & movement of system
• Precipitation of convective nature & spatially variable with localized higher amounts possible
THE ADJUSTMENT PHASE Case Study May 18-19, 1999
• Adjust guidance/Ascertain Uncertainty
• Significant Event– Predictability high…local analysis corroborated
guidance/uncertainty smaller
• “Working PQPF”…includes amounts & uncertainties
THE INTEGRATION PHASE Case Study May 18-19, 1999
• Integrate “Working PQPF”, local influences & LCG
• Uncertainty small…tend toward “Working PQPF”
24hour POP24hour POP
X50X50
X50X50
X25X25
X25X25
X75X75
X75X75
T50
T50
Z1Z1
Z1Z1
Z2Z2
Z3Z3
Z4Z4
Summary of Case Study May 18-19, 1999Well Organized Frontal System
• Precipitation probable & significant.
• Predictability of pattern high…models in agreement. Analysis corroborate guidance.
• Convective nature, spatially variable, localized higher amounts possible.
• Uncertainty reflected in wide credible interval.
WFOWFOMosaicMosaic
Stage 3Stage 3PrecipPrecip(actual)(actual)
Summary of Case Study May 18-19, 1999Monongahela River Basin
24-h period ending 1200 UTC 5/19/99
Exceedance Fractiles Expected Fractions(inches) (%)
X75 X50 X25Z1 Z2 Z3 Z4
PQPF .54 1.10 2.00 10 30 50 10
LCG* .34 0.47 0.74 28 20 21 31
*LCG estimates are conditioned on a minimum of 0.25 inches.
ACTUAL 0.31 0 7 93 0
PoP = 100%
Probabilistic River Stage Forecast
(PRSF)
PRSF Methodology
• Interfaces with NWSRFS– Ensemble Streamflow Prediction (ESP) - OH– Bayesian Forecast System (BFS) - UVA
• Output – Exceedance Function– Quantifies total uncertainty about river stage
for a certain day
Integration of PRSF System with NWSRFS
Gridded PQPF
RFC WFO
Preprocessing to getDeterministic QPF
PrecipitationForecast Processor
PFP
River Forecast Viewer
OperationalForecast SystemNWSRFS - OFS
EnsembleStreamflow Prediction
NWSRFS - ESP
Bayesian Forecasting System
BFS
River Forecast Interface
RFI
River Forecast ViewerRFV
WFO Web Site
End-User
Bayesian Forecast SystemFrom NWSRFS: Input for forecast point
PrecipitationUncertaintyProcessor(PUP)
HydrologicUncertaintyProcessor(HUP)
Integrator(INT)
InteractiveReview andAdjustment
(IRA)
Parameter estimatesFrom off-line
simulation
Guidance PRSF
Model PRSF
RIVER FORECAST INTERFACE
GRAPHICAL RIVER FORECAST INTERFACE
• Input - Probabilistic River Stage Forecasts (PRSF)
• Purpose– Display PRSF– Aid forecaster in deciding flood alarm
(watch/warning)– Communicate flood alarms to users– Aid users in making decisions based on PRSF
SUMMARY
• Provided overview of Probabilistic Hydrometeorological Forecasting System
• Focused on PQPF – Methodology– Interactive Software– Probabilistic Reasoning
• Demonstrated concepts with May18-19, 1999 Case Study
PQPF Lab Exercise
Objective:Prepare a probabilistic QPF of spatially averaged precipitation over fourriver basis to determine how well calibrated the forecasts aft for the class as a whole.
Instructions:Review the Hurricane Floyd case using any available data through 12zon 16 Sep 1999. Prepare probabilistic QPFs of spatially averaged precipitation for the 24 hour period ending on 17 Sep 1999 for eachof the four basins on your lab sheet. For X75, X50, and X25 enter thevalue to the nearest tenth of an inch. For Z(1,2,3,4) enter the percentage of the total rainfall that occurred in each time period.
PQPF LAB EXERCISE
BASIN X75 X50 X25 Z1 Z2 Z3 Z416/12Z-18Z 16/18Z-7/00Z 17/00Z-06Z 17/06Z-12Z
PASSAIC
RARITAN
SCHUYLKILL
SOUTHEAST PA/LWR DELAWARE
7.84
7.34
6.69
8.09
7.76
7.84
6.84
8.23
7.67
7.25
7.43
6.93
7.56
7.67
4.37
3.76
4.44
5.28
8.31
6.66
5.60
6.03
X50 Verification
River X50 Z1 Z2 Z3 Z4
PASSAIC 7.59 34 58 8 0
RARITAN 7.36 46 51 1 2
SCHUYLKILL 5.47 47 50 3 0
SE PA/DELAWARE 5.80 53 45 1 1