Use of HPC Confidence Use of HPC Confidence Interval Forecasts to Interval Forecasts to Produce a Hydrologic Produce a Hydrologic

Ensemble of River Ensemble of River ForecastsForecasts

John HalquistJohn HalquistNOAA / NWS / NCRFCNOAA / NWS / NCRFC

Chanhassen, MNChanhassen, MN

The problem:The problem: River Forecasts (deterministic) are typically River Forecasts (deterministic) are typically

based on one possible hydrometeorologic based on one possible hydrometeorologic scenarioscenario

Changing or dynamic weather patterns result Changing or dynamic weather patterns result in different rainfall amounts or distribution than in different rainfall amounts or distribution than forecastforecast

Users want access to more potential scenariosUsers want access to more potential scenarios Some want more future rain, while others want lessSome want more future rain, while others want less

A solution:A solution: Use additional possible Quantitative Use additional possible Quantitative

Precipitation Forecasts (QPF) to produce Precipitation Forecasts (QPF) to produce an ensemble of possible River Forecastsan ensemble of possible River Forecasts

Maintain connection to realistic Maintain connection to realistic meteorologic conditionsmeteorologic conditions

Utilize Short Range Ensemble Forecasts Utilize Short Range Ensemble Forecasts (SREFs) and Hydrometeorological (SREFs) and Hydrometeorological Prediction Center (HPC) expertisePrediction Center (HPC) expertise

HPC Confidence Interval HPC Confidence Interval QPFQPF

Confidence Intervals (CI) derived by Confidence Intervals (CI) derived by analyzing SREF QPF spread and HPC analyzing SREF QPF spread and HPC QPF absolute errors (AE)QPF absolute errors (AE)

95% Confidence Interval QPF 95% Confidence Interval QPF calculated twice per day (1200 and calculated twice per day (1200 and 0000 UTC)0000 UTC)

HPC Confidence Interval HPC Confidence Interval QPFQPF

River Forecast EnsembleRiver Forecast Ensemble Mean areal QPF are computed from the Mean areal QPF are computed from the

HPC 95% CI QPF – Maximum and MinimumHPC 95% CI QPF – Maximum and Minimum Independent hydrologic model simulations Independent hydrologic model simulations

are produced using these QPF as inputare produced using these QPF as input Resultant hydrologic time-series are Resultant hydrologic time-series are

provided in Scalable Vector Graphics (SVG) provided in Scalable Vector Graphics (SVG) Allows for interactive query of data Allows for interactive query of data

represented in plotsrepresented in plots

Sample ensemble displaySample ensemble display

Observed data

Hydrograph w/HPC 95% CI Minimum QPF

Hydrograph w/HPC 95% CI Maximum QPF

Hydrograph w/ HPC deterministic QPF

Mean Areal QPF (local)

Example eventExample eventForecast, Model and Observed hydrographs for CIDI4 - June 25, 2005

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6/25 0:00 6/26 0:00 6/27 0:00 6/28 0:00 6/29 0:00 6/30 0:00 7/1 0:00 7/2 0:00 7/3 0:00

Date / Time (UTC)

Stag

e (f

t)

QPFCN QPFCX HQPF Forecast Observed

Observed

TraditionalForecast

AnalysisAnalysis Performed for April Performed for April

– September 2005– September 2005 Locations: Locations:

Cedar River, IowaCedar River, Iowa 11,593 forecast vs 11,593 forecast vs

observation pairsobservation pairs 49,211 modeled vs 49,211 modeled vs

observation pairsobservation pairs

AnalysisAnalysis Measures:Measures:

BIASBIAS Probability of Detection (POD)Probability of Detection (POD) False Alarm Ratio (FAR)False Alarm Ratio (FAR) Critical Success Index (CSI)Critical Success Index (CSI) Percent Correct (PC)Percent Correct (PC) Mean Error (ME)Mean Error (ME) Mean Absolute Error (MAE)Mean Absolute Error (MAE) Root Mean Square Error (RMSE)Root Mean Square Error (RMSE)

AnalysisAnalysisCombined dataset  Forecast

11,593 points

HQPF49,211 pts.

QPFCN49,211

pts.

QPFCX49,211

pts.BIAS 0.874 0.855 0.791 1.068POD 0.773 0.777 0.747 0.819FAR 0.115 0.091 0.056 0.233CSI 0.702 0.721 0.715 0.656 PC 70.229 72.052 71.490 65.618ME -0.132 -0.201 -0.286 0.170MAE 0.384 0.389 0.397 0.580RMSE 0.724 0.777 0.797 1.297

Std error: .7822R2 : .9197

Std error: 1.198

R2 : .1419Std error: .7822R2 : .9197

What next?What next? Proceed and provide ensembles for Proceed and provide ensembles for

representative locations to WFOsrepresentative locations to WFOs Continue evaluationContinue evaluation Add locationsAdd locations Investigate additional ensemble membersInvestigate additional ensemble members

Forecast temperatures Forecast temperatures Additional hours of QPFAdditional hours of QPF QPF time shiftingQPF time shifting