Tubing: An Alternative to Clustering for the Classification of Ensemble Forecasts

Abstract

Tubing is a method of classification of meteorological forecasts. The method has been designed to facilitate a human interpretation of the distribution of forecasts produced by an ensemble prediction system (EPS). This interpretation aims to complement probabilistic forecasts generated from EPS weather parameter probability distributions. Ensemble forecasts are generally classified according to their similarities. On the other hand, ensemble distributions rarely prove multimodal in practice. The tubing method disregards possible modes and gives instead more emphasis to the central part of the distribution where the ensemble mean is located. Ensemble forecasts are then classified according to the way they differ from the ensemble mean. The tubing algorithm first groups the members lying around the ensemble mean into the central cluster. Remaining ensemble members are classified into a number of tubes. A tube is a cylinder ranging from the central cluster to an extreme member of the distribution. The central cluster is represented by its centroid, meant to indicate the meteorological pattern that is the most likely to verify. Tubes are represented by their extreme members, full resolution representatives of possible deviations from the main scenario indicated by the central cluster.