Using the Hydrologic Ensemble Forecast Service (HEFS)

### Produced by The COMET® Program

### 6.0 Summary

Displays and guidance from the HEFS offer several advantages to operational forecasters and users of flow and stage forecasts due to the ability to express uncertainty, correct for biases, and provide probabilistic guidance across a range of conditions. In addition, the HEFS can give greater lead times for potential events than previous NWS hydrologic forecast systems because it uses QPF inputs across a range of time steps, while accounting for the uncertainties in those inputs.

Products and forecast displays from the HEFS will continue to evolve after the publication of this lesson. The full set of HEFS products will do the following:

- Provide seamless hydrologic forecast guidance from hours to years
- Use QPF input across multiple time scales
- Provide longer lead-time time evolution of major hydrologic events
- Quantify the combined uncertainty from both meteorological forcing and hydrologic modeling while correcting for biases
- Allow decision making about possible outcomes based on probabilistic guidance
- Evolve to include a wide array of user-tailored products, including standard verification