User's Guide

Probabilistic River Stage Forecast

The forecasted variable is the river stage to be observed at a forecast point at 7:00 am on day n (n = 1,2,3), counted from the day on which the forecast is prepared. [The observation time is 8:00 am during teh daylight savings period.]

Because future precipitation input to the basin above the forecast point is uncertain and the hydrologic model that simulates the basin response is imperfect, the future river stage is uncertain as well. The probabilistic river stage forecast (PRSF) quantifies the total uncertainty about the river stage.

The PRSF is based upon (1) a probabilistic quantitative precipitation forecast (PQPF) for the next 24 hours, (2) a simulation of the basin response to possible precipitation inputs, given the current initial conditions of the basin, and (3) a probabilistic quantification of all other uncertainties, which may result from model, parameter, estimation, and measurement errors.

For each of the three future days, the PRSF system outputs a probability distribution of the river stage. The distributions are converted into graphics. The user's guide explains five graphics:

Key

Exceedance Function

Flood Alarm

Isoprobability Time Series

Cross Section

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