National Weather Service
Professional Development Series
Professional Competency Unit

Hydrologic Forecasting

PCU 11: Conducting Hydrologic Forecast Verification

Producer: Tim Helble - Hydrologic Services Division
Office of Climate, Water, and Weather Services

Description of Job Duty Competency to be Achieved

Use procedures required for the verification of hydrologic forecasts for the short-range forecast horizon.

Description of Need

Forecast verification is required by NWS management to document improvements in hydrologic prediction services. The nationally-supported hydrologic forecast verification system is highly automated, but forecasters must be able to monitor system performance, know how to generate and interpret verification statistics when needed, and use them to improve hydrologic forecast operations for all time scales.

Specific Job Task Skills and Knowledge

1. Know the roles of NWS field and headquarters offices in the National Hydrologic Forecast Verification Program.

2. Use the verification system to compute statistics and know how to interpret and apply them.

3. Account for the sources of error and uncertainty in hydrologic forecasts.

4. Provide basic support for verification software and databases.

Instructional Components

Instructional Component 11.1: - Workshop: Hydrologic Forecast Verification/Validation. This workshop covers the use of hydrologic forecast verification procedures. Techniques for assessing the accuracy of hydrologic forecasts (both deterministic and ensemble-based) before they are issued are also covered.

Instructional Component 11.2 - Workshop: Statistical Hydrology. This workshop will give hydrologic forecasters a good working knowledge of the uncertainties in predicting hydrologic variables so they will be better prepared to function in two areas which will become increasingly important to the Hydrologic Services Program - verification and hydrologic forecasts which quantify uncertainty. This workshop will focus on the following:

  • Basic concepts of probability and statistics, sampling theory, and analysis techniques.
  • Variable, time series, and temporal relationships - using techniques such as harmonic analysis to differentiate between data error and noise.
  • Statistical analysis of extreme events - e.g., trend analysis, testing for seasonability of forecasts.
  • The randomness of the precipitation, temperature, and soil data.
  • Sampling and measurement errors.
  • Errors of the models describing the predicting of the physical processes.

    • Application of these principles to short-range deterministic forecasting (i.e., NWSRFS IFP) and extended-range ensemble forecasting (i.e., ESP) will be discussed. Statistical water supply may be discussed as an example of how statistics can be used in hydrological forecasting, but details of SWS will be covered the ESP/SWS workshop.

    Instructional Component 11.3 - On-Station Training: Forecast Verification. Each field office will provide training on local and/or regional verification operations conducted in addition to those for the National Hydrologic Forecast Verification Program.

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    Last Reviewed or Updated on 2/22/01