Sea level probability forecasts

Introduction

Traditionally, forecast models produce a single value for any predictand for a certain forecast range: the deterministic forecast. A forecaster would then have an idea of the accuracy from verification of forecasts from the past or from experience.
Developments over the last decade, however, have made it possible to add uncertainty information to the forecasts, and this information even finds its way to the general public nowadays. Well known is the ECMWF Ensemble Prediction System, which has recently been extended from 10 to 15 days.

Sea levels

Forecasts for water levels on the North Sea are produced by the WAQUA/DCSM model, a joint effort of RIKZ and KNMI. The standard version produces deterministic forecasts and is driven by 10 m winds and sea level pressure from KNMI's Hirlam model.
But there are more possibilities: ECMWF's deterministic model and Ensemble Prediction System would allow forecasts up to 15 days and provide uncertainty information beyond 48 hours. Using the SRNWP-PEPS ensemble as input for WAQUA/DCSM would provide uncertianty information for the first 48 hours. Also the multi-model ensemble of water level forecasts from Institutes around the North Sea gives information on the accuracy of each of the individual forecasts.
Users of the forecasts have explicitly expressed interest in such extensions of the model forecasts.

Using ECMWF

As a first step, ECMWF model results are being used to drive WAQUA/DCSM and produce both deterministic water level forecasts and water level ensembles. Actual forecasts can be found in the menu on the right.