Water Supply Outlooks are seasonal volume forecasts, generally for the period April to September.
These outlooks are generally intended for water users such as irrigators.
The forecasts are volumes of flow, in acre-feet, which are expected to flow by a given point during a snowmelt season.
Spring Flood Forecasts are developed each spring by the NWS for areas subject to snowmelt floods and are intended to forecast maximum peak flows and stages from spring snowmelt conditions.
Spring Flood Forecasts start with current conditions as reflected in the forecast model.
Current conditions include actual streamflows, soil moisture conditions, and snow cover water equivalents.
Historical melt patterns and forecast temperatures are then applied and the forecast models run into the future far enough to melt snowcover.
Projected peak flows are extracted in the process and constitute the Spring Flood Forecasts.

Ensemble Streamflow Prediction (ESP), combines the needs of Water Supply Outlooks and Spring Flood Outlooks into a single forecast process which may meet both needs.
ESP starts with current hydrologic conditions.
Then, a series of historical data in the form of observed precipitation and temperature patterns are applied to run the forecast model into the future through the snowmelt runoff period.
By doing this for many years of historical data, statements can be made concerning probabilities of volumes of runoff and peak flows which can be anticipated.