Proceedings - C-SRNWP Project

Verification of COSMO LEPS
The COSMO LEPS has been verified with respect to several parameters and regions. The
most interesting and spatially variable is indeed precipitation. In order to acquire knowledge
on the observed precipitation at high resolution, it is important to gather also non-synoptic
sums from rain gauges, usually 12 or 24 hour sums. Since the configuration of the system
changed in February 2006, the verification period is rather short. The old system (10
members, 10 km resolutions 32 levels) showed the following features: the ECMF EPS is
usually slightly better for low thresholds, (frequent events), but the COSMO LEPS is clearly
better for high thresholds (rare events). For precipitation the crossover typically happens at
around 10mm/day.
As an example of verification from spring 2006, we show the amount of outliers in 24 hour
precipitation carried out by C. Marsigli at ARPA SIM. The observations come from the high
resolution rain gauges of Germany, Switzerland and northern Italy. The outliers are defined as
the proportion of observations lying outside the ensemble. The gain of the COSMO LEPS
over the same size ECMWF EPS is evident. The reason comes from the ability of the
COSMO LEPS to produce more localized precipitations and also to predict better higher
amounts.
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