Verification of global and regional NWP models over South America

Abstract

South America has received less attention from the global numerical weather prediction community than many other regions. This is reflected, for example, in its absence as a region in the standardised WMO verification score exchange. As a result, global modelling centres may have missed out on interesting scientific challenges, and potential insights, in a unique testing ground in one of the few land masses in the Southern Hemisphere. To address this situation, a pilot project was launched in early 2024 by the Working Group on Numerical Experimentation (WGNE) and the Joint Working Group on Forecast Verification Research (JWGFVR), partly in response to the requirements of the United Nations Early Warnings for All initiative (EW4All). This pilot project, led by the Argentine National Meteorological Service (SMN) and the European Centre for Medium Range Forecasting (ECMWF), aims to explore the performance of global and regional forecasts over South America and their potential as early warning tools. For the sake of simplicity, we have focused mainly on the territory of Argentina and on deterministic operational forecasts. This Technical Memorandum presents the first results of the pilot project, focusing on two perspectives: a general statistical verification of the ECMWF Integrated Forecasting System (IFS) control operational forecast, and an in-depth evaluation of model performance in three individual High Impact Weather (HIW) events which, due to their characteristics, are both of societal relevance and posing a challenge to models. Within the first perspective, temporally and/or spatially aggregated summary verification statistics are produced for upper air variables by comparing forecasts with their own analysis, and for surface variables by comparing surface forecast fields with SYNOP station data. In addition, the IFS deterministic operational forecast is compared with other global models and with a limited area model over the South America region. Within the second perspective, three individual case studies covering HIW events with very different characteristics are analysed: a convective storm causing severe wind damage and loss of life, a strong Zonda wind (Foehn) on the lee side of the Andes, and a prolonged heat wave.