The intense precipitation event that occurred between 3 and 6 November 1994 and caused extensive flooding over Piedmont in northwestern Italy is simulated and tested with respect to various physical aspects, using a meteorological mesoscale model (BOLAM). The period when the most intense rain occurred, mainly covering the second half of 4 and all of 5 November, is examined. A control experiment, starting at 1200 UTC 4 November, simulates the two observed precipitation peaks and captures the magnitude and timing of the most intense precipitation well even at relatively low horizontal resolution (about 30 km). The European Centre for Medium-Range Weather Forecasts analyses are used to provide the initial and boundary conditions. Model output diagnostics and comparison with observations indicate that most of the precipitation is associated with a prefrontal low-level jet, ahead of the cold front, impinging upon the orography of the region (Alps and Apennines). The model simulates a multiple rainband... Abstract The intense precipitation event that occurred between 3 and 6 November 1994 and caused extensive flooding over Piedmont in northwestern Italy is simulated and tested with respect to various physical aspects, using a meteorological mesoscale model (BOLAM). The period when the most intense rain occurred, mainly covering the second half of 4 and all of 5 November, is examined. A control experiment, starting at 1200 UTC 4 November, simulates the two observed precipitation peaks and captures the magnitude and timing of the most intense precipitation well even at relatively low horizontal resolution (about 30 km). The European Centre for Medium-Range Weather Forecasts analyses are used to provide the initial and boundary conditions. Model output diagnostics and comparison with observations indicate that most of the precipitation is associated with a prefrontal low-level jet, ahead of the cold front, impinging upon the orography of the region (Alps and Apennines). The model simulates a multiple rainband...

In this paper, the sensitivities of the equitable threat score (ETS) and the true skill score (TSS), obtained with a 2 3 2 contingency table, to continuous precipitation forecast errors are investigated. Two idealized error models are adopted to describe the difference between forecasts and perfect observations. The ob- servations consist of a time series generated by a multiplicative cascade model. The forecasts are constructed by adding the modeled errors to the observations. Two examples that are representative of two precipitation regimes are considered. Monte Carlo simulations of the modeled errors are performed to compute the score uncertainties. Monotonic relationships between the precipitation forecast errors and the two skill scores are found. It is shown that the precipitation regime and the event frequency influence these relationships and the score uncertainties. The score uncertainties also depend on the forecast errors. Furthermore, it is shown that a relationship exists between the ETS and TSS when the forecast errors are very large. Results suggest that more information should be provided together with the scores and their uncertainties in order to provide a complete picture of the forecast performance

A previsional system for the forecast of the state of the Mediterranean Sea and of surges in the northern Adriatic Sea has been designed and tested. The system consists of a limited area model (the Bologna Limited Area Model, BOLAM), which computes high-resolution pressure and surface wind fields, to serve as the input of a wave model (WAM) and of a shallow water model (two-dimensional Princeton Ocean Model, POM-2D). Results of two case studies are presented, chosen to test the ability of the system to predict extreme surge events originating from cyclonic circulation over the Mediterranean basin. The two case studies cover the periods 4–9 October 1998 and 11–22 November 1996. Comparison with observed buoy data shows that the results of the WAM simulations forced by the wind fields obtained from the high-resolution BOLAM model are significantly better than those obtained using a lower-resolution forcing from the ECMWF analyses. Two domains corresponding to the entire Mediterranean basin and to th... Abstract A previsional system for the forecast of the state of the Mediterranean Sea and of surges in the northern Adriatic Sea has been designed and tested. The system consists of a limited area model (the Bologna Limited Area Model, BOLAM), which computes high-resolution pressure and surface wind fields, to serve as the input of a wave model (WAM) and of a shallow water model (two-dimensional Princeton Ocean Model, POM-2D). Results of two case studies are presented, chosen to test the ability of the system to predict extreme surge events originating from cyclonic circulation over the Mediterranean basin. The two case studies cover the periods 4–9 October 1998 and 11–22 November 1996. Comparison with observed buoy data shows that the results of the WAM simulations forced by the wind fields obtained from the high-resolution BOLAM model are significantly better than those obtained using a lower-resolution forcing from the ECMWF analyses. Two domains corresponding to the entire Mediterranean basin and to th...

The speed of Atlantic surface depressions, occurred during the autumn and winter seasons and that lead to intense precipitation over Italy from 1951 to 2000, was investigated. Italy was divided into 5 regions as documented in previous climatological studies (based on Principal Component Analysis). Intense precipitation events were selected on the basis of in situ rain gauge data and clustered according to the region that they hit. For each intense precipitation event we tried to identify an associated surface depression and we tracked it, within a large domain covering the Mediterranean and Atlantic regions, from its formation to cyclolysis in order to estimate its speed. "Depression speeds" were estimated with 6-h resolution and clustered into slow and non-slow classes by means of a threshold, coinciding with the first quartile of speed distribution and depression centre speeds were associated with their positions. Slow speeds occurring over an area including Italy and the western Mediterranean basin showed frequencies higher than 25%, for all the Italian regions but one. The probability of obtaining by chance the observed more than 25% success rate was estimated by means of a binomial distribution. The statistical reliability of the result is confirmed for only one region. For Italy as a whole, results were confirmed at 95% confidence level. Stability of the statistical inference, with respect to errors in estimating depression speed and changes in the threshold of slow depressions, was analysed and essentially confirmed the previous results.

Verification of modeled rainfall with precipitation observed by a rain gauge network has been performed in a case study over the Cyprus Island. Cyprus has a relatively dense rain gauge network. The applied verification method is the Contiguous Rain Area (CRA) analysis. Some drawbacks of the CRA method are pointed out when it is applied to such a case study. Impact on the CRA results, when considering different dimensions of the verification sub-domain and different types of indicators (correlation and mean square error) used in the comparison, are discussed. Results indicate that care should be taken when verification of modeled rainfall is performed over a domain smaller than the model one.

Many ‘high-impact’ meteorological, marine and hydrological events in the Mediterranean area are characterized by horizontal spatial scales of the order of 10–100 km. Such events are, sometimes, driven by complex dynamical processes involving planetary scale atmospheric flows. Several international programs (ALPEX, POEM, MAP, PYREX, MEDEX) have improved the understanding of some of these processes. However, because of the Mediterranean's geomorphological structure, characterized by mountain chains (e.g. the Alps), semi-enclosed sea basins and small river catchments, many problems remain. It is clear that such problems have to be faced in the context of analysis-prediction systems bridging the gap between global and local scales of motion. These systems should allow for an adequate representation of key dynamical processes at all the relevant scales of motion. The Hydro-Meteorological-Marine System (‘Sistema Idro-Meteo-Mare’, SIMM) is a first step in developing an integrated system, adequately covering all scales of motion from global to local. A short description of the system is presented, highlighting scientific concepts behind design choices. A summary of the results of verification tests is also illustrated, together with a general evaluation of the whole process in planning, developing and running SIMM in order to assist future updates of the system, currently under development. Copyright © 2007 Royal Meteorological Society