Using the Hydrologic Ensemble Forecast Service (HEFS)

4.0 The Hydrologic Ensemble Forecast Service (HEFS) » 4.4 The HEFS Compared to Previous Guidance

Goal: Improve NWS Hydrologic Services

Feature

EPS (Old Service)

HEFS (New Service)

Forecast Time Horizon

Weeks to seasons

Hours to years, depending on the input forecasts

Input Forecasting (“Forcing”)

Historical climate data (i.e. weather observations) with some variations between RFCs

Short-, medium-, and long-range weather forecasts

Uncertainty Modeling

Climate-based; no accounting for hydrologic uncertainty or bias; suitable for long-range forecasting only

Captures uncertainty from multiple sources and corrects for biases in forcing and flow at all forecast lead times

Products

Limited number of graphical products (focused on long-range) and verification

A wide array of data and user-tailored products are planned, including standard verification

Until recently, NWS ensemble streamflow forecasts within NOAA’s Advanced Hydrologic PredictionService (AHPS) were produced exclusively with the Ensemble Streamflow Prediction (ESP) system. The HEFS offers advances in ensemble forecasting that were lacking in ESP, such as:

  • Use of short, medium, and long-range NWP model forecasts, such as QPF
  • More comprehensive accounting for uncertainty from both the meteorological forcing and the hydrologic modeling
  • More products, including verification and user-tailored products