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Volume 138, Issue 665 p. 1072-1082
Research Article

Nowcasting of precipitation by an NWP model using assimilation of extrapolated radar reflectivity

Zbynek Sokol

Corresponding Author

Zbynek Sokol

Institute of Atmospheric Physics, Academy of Sciences, Prague, Czech Republic

Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic, Bocni II 1401, Prague 14131, Czech Republic.Search for more papers by this author
Petr Zacharov

Petr Zacharov

Institute of Atmospheric Physics, Academy of Sciences, Prague, Czech Republic

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First published: 22 November 2011
Citations: 28

Abstract

Two methods for assimilating radar reflectivity into the COSMO numerical weather prediction (NWP) model were compared to precipitation forecasts. The first method assimilated observed radar reflectivity, and the second one assimilated observed and extrapolated radar reflectivity. The assimilation technique was based on the correction of the model's water vapour mixing ratio. The extrapolation was performed by the COTREC method and was 1 hour long. The model's horizontal resolution was 2.8 km.

The comparison of methods was based on verification of the observed and forecast hourly precipitation. The comparison was performed for the 1st, 2nd and 3rd hours of each forecast. On the whole, 45 forecasts from nine days of convective precipitation were evaluated for each hour. The evaluation included subjective verification and the following objective skill scores: Fractions Skill Scores, SAL and a measure based on a categorical-probabilistic approach.

The results confirmed that assimilation complemented by the extrapolated data improves the accuracy of precipitation forecasts. The improvement was obvious in a majority of the single forecasts studied, and it is confirmed by all evaluation techniques. COSMO forecasts that used the extrapolation showed reasonable competence in forecasting for the first and the second hours. Copyright © 2011 Royal Meteorological Society