Intercomparison of global model precipitation forecast skill in 2010/11 using the SEEPS score

TitleIntercomparison of global model precipitation forecast skill in 2010/11 using the SEEPS score
Publication TypeTechnical memorandum
Date Published01/2012
Secondary TitleECMWF Technical Memoranda
AuthorsHaiden, T, Rodwell, M, Richardson, D, Okagaki, A, Robinson, T, Hewson, T

Precipitation forecasts from five global numerical weather prediction (NWP) models are verified against raingauge observations using the new Stable Equitable Error in Probability Space (SEEPS) score. It is based on a 3×3 contingency table and measures the ability of a forecast to discriminate between ‘dry', ‘light precipitation', and ‘heavy precipitation'. In SEEPS, the threshold defining the boundary between the ‘light' and ‘heavy' categories varies systematically with precipitation climate. Results obtained for SEEPS are compared to those of more well-known scores, and are broken down with regard to individual contributions from the contingency table. It is found that differences in skill between the models are consistent for different scores, but are small compared to seasonal and geographical variations, which themselves can be largely ascribed to the varying prevalence of deep convection. Differences between the tropics and extra-tropics are quite pronounced. SEEPS scores at forecast day 1 in the tropics are similar to those at day 6 in the extra-tropics. It is found that the model ranking is robust with respect to choices in the score computation. The issue of observation representativeness is addressed using a ‘quasi-perfect model' approach. Results suggest that just under one-half of the current forecast error at day 1 in the extra-tropics can be attributed to the fact that grid-box values are verified against point observations.

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