Verification of hydrologic forecasts provides valuable information for both the forecasters and the users of the forecasts.

This information can be used by both of these groups to help with evaluating, improving, and using the forecast products.

Hydrologic forecast verification can apply to a variety of hydrologic concerns such as snowmelt runoff, water supply, and all categories of stream flows, including floods and low flows.

Verification Topics

• Distribution Properties
• Forecast Confidence
• Correlation
• Categorical Forecasts
• Accuracy (Error Statistics)
• Forecast Skill
• Conditional Verification

This module will review and explain the statistical measures and graphic displays associated with seven topics in hydrologic verification. These topics were defined by the National Weather Service (NWS) Verification Systems Requirements team and are covered in sections 2 through 8 of this module.

This section reviews the reasons to verify forecasts and introduces important concepts and terminology. We will examine the following questions:

• Why do we verify hydrologic forecasts?
• Why can't one number tell the whole story?
• What is a "good" forecast?
• What types of hydrologic forecasts are verified?
• What are the commonly used verification measures?
• What are the seven verification topics used by the NWS Verification Systems Requirements Team?