Seven years of activity in the field of mesoscale ensemble forecasting by the COSMO-LEPS system: main achievements and open challenges

Abstract

A B S T R A C TIn this work, the main characteristics of COSMO-LEPS, the Limited-area Ensemble Prediction System developed in the framework of the COnsortium for Small-scale MOdelling, are presented. The present status of the system is shown with the description of the methodology and of the main upgrades which took place during its years of activity. The performance of COSMO-LEPS for the probabilistic prediction of precipitation is assessed in terms of both time-series and seasonal scores over a 7-yr period. A fixed number of stations are selected and observations are compared to short and early medium-range forecasts. Different verification indices are used to assess the skill of COSMO-LEPS and to identify the impact of system modifications on forecast skill. The different system upgrades are found to impact positively on COSMO-LEPS performance, with a gain of 2 d of predictability in the last 4 yr of operational forecasts. This holds when the skill of the system is assessed both for single events (e.g. precipitation surpassing a fixed threshold) and for multi-event situations. Scores for fixed forecast ranges but varying thresholds confirm increasingly better performance of the system. For a few seasons, the performance of COSMO-LEPS is also assessed in terms of probabilistic prediction of some upper-air variables. Then, the skill of COSMO-LEPS is compared to that of the global-ensemble system providing the boundaries, to identify the extent to which skill improvements may relate to those of the driving ensemble. Finally, the main streams of development for COSMO-LEPS system are discussed with future possible upgrades and methodology modifications.

The potential of radar-based ensemble forecasts for flash-flood early warning in the southern Swiss Alps

“…They are run at different spatial and temporal resolutions, typically ranging from about 2 to 20 km and from 24 to 240 h of lead time (Montani et al, 2011;Zappa et al, 2008;Price et al, 2012a). One of the most detailed models available in Europe is the COSMO-2, which has a grid size of 2.2 km and 24 h of lead time computed every 3 h (Weusthoff et al, 2010;Ament et al, 2011).…”

Uncertainty propagation for flood forecasting in the Alps: different views and impacts from MAP D-PHASE

“…This suggests that objective verification scores do not always truly reflect the actual meteorological situation as sought by forecasters. Also, the forecasters appreciated the availability of singlemodel ensemble information (such as from the limited area model COSMO-LEPS (Marsigli et al, 2005;Montani et al, 2001Montani et al, , 2011) much more than having at their disposition a multitude of different deterministic high-resolution models. While the "ensemble judgment" has to be made by the user him/herself in the latter case, apparently the usual probabilistic output (probability maps, etc.)…”

Sensitivity of sea-level forecasting to the horizontal resolution and sea surface forcing for different configurations of an oceanographic model of the Adriatic Sea

“…It is thus possible to compare the differences between the effects on the grid resolution only, and the effects on the two different model configurations separately. Additionally, in order to evaluate the meteorological forcing effect, the Aop and Ah models have been run in ensemble mode, forced by the Arpae 16-members COSMO-LEPS ensemble system (Montani et al, 2011). All test runs have a forecast length of +96 h. The list of simulations presented in this study are summarized in Table 1.…”