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The celebration of the 25th anniversary of the Piedmont flood was organized by the University of Piemonte Orientale in Alessandria, a town that was severely affected in November 1994. It has been an opportunity to reexamine the meteorological event and assess the potential of CNR-ISAC models, after more than 20 years of development, to accurately simulate the heavy precipitation at different lead times. The predictability of this extreme event has been studied on a wide range of space and time scales, from subseasonal to convection resolving, using a variety of model setups and initial conditions. The subseasonal experiment produces a precipitation anomaly that, even if underestimated, indicates some predictability beyond the second forecast week. At shorter ranges, results indicate that there is a consistent improvement in the precipitation forecast going from low-resolution hydrostatic to high-resolution nonhydrostatic models. It is only at very high resolution (500 m) that the convective activity extending to the north of the divide line of the Ligurian Apennines, which was responsible for the flood of the Tanaro River, is predicted with an intensity comparable with rain gauge observations. The main mesoscale phenomena that played a role in the different phases of the event have been also identified.

Although the phenomenon has been known, and investigated, as early as the nineteenth century, the interest in understanding Alpine lee cyclogenesis (often called Genoa cyclogenesis) has grown since the middle twentieth century, when it was realized that the largest fraction of cyclones affecting the central-eastern Mediterranean and later Eastern Europe originated in the area south of the Alps, more often in the Gulf of Genoa. Forecasting this type of cyclogenesis remained a challenging task until at least the mid- late 1980s, even after the development of the earlier NWP models, which failed in predicting this phenomenon, lacking the ability to adequately represent the orographic forcing. Monitoring and understanding of cyclogenesis in the lee of the Alps was the main objective of field projects, the most important being GARP-ALPEX in 1982. The following years were full of ideas and theories about this phenomenon, which is representative of orographic cyclogenesis in other regions of the world. The main steps in understanding the complex phenomenon of lee cyclogenesis, with particular reference to the Alps, are outlined here, focusing on theoretical explanations.

Natural processes and human activities are strongly connected, and sometimes con icting, in the evolution of coastal and transitional environments. The strong anthropic pressure on coastal regions, together with the e ects of a changing climate, demands nowadays more pressingly for e cient tools to characterise and predict the behaviour of such systems in order to de ne appropriate response strategies. This requires a deep understanding of the connections among di erent drivers and di erent scales, a multidisciplinary challenge in which heterogeneous data, approaches and scales need to be framed within a consistent dynamical description. To this aim, a speci c research line was dedicated to “Coastal Vulnerability to Erosion and Sea Level Rise” within the RITMARE Project, supported by the Italian Ministry of University and Research with the purpose of integrating the Italian Marine community in shared research elds in the period 2012-2017. The activities carried out in this framework have been moving along interconnected branches tackling the themes related with sea level rise, ocean modelling, and geomorphological assessment in present conditions and in di erent climate change scenarios, with an eye on the exploitation of marine sand as a strategic resource. In this contribution we review the main outcomes of this multidisciplinary and coordinated research. Besides discussing the advances and the possibilities from state-of-the art technologies and methodologies, we point out that a coordinated use of the described tools should be promoted in the design of survey and monitoring activities, as well as in the exploitation of already collected data. Expected outcomes of this strategy include the implementation of improved policies and infrastructures for coastal protection, anked by reliable short-term forecasting systems and e cient rapid response protocols, in the framework of an integrated coastal planning at the multi-decadal scale.

The first Special Observation Period (SOP1) field campaign of the HyMeX (HYdrological cycle in the Mediterranean EXperiment) program was held in fall 2012 and was devoted to the investigation of heavy precipitation and floods in the Western Mediterranean. Both the Italian research and operational meteorological communities actively participated by providing a valuable contribution through the organization of an ad hoc national Operational Centre. The paper presents an overview of this participation, resulting in a fruitful multidisciplinary experience able to build a bridge between academia, researchers, forecasters, end-users and decision makers. The benefits provided by the wide national involvement and the consequent possible national impacts and progress are discussed within the context of the complex organization of meteorology in Italy.

The increasing awareness of the potential threats acting on the coastal regions, combined with the intense anthropic pressure and the broad variety of socio-economic drivers acting on these systems, bestowed progressively stronger emphasis to the development of sound planning and management policies. The assessment and the formulation of plans for the response to coastal morphological vulnerability is a multidisciplinary challenge, in which different typology of information, approaches and scales need to be integrated and framed within a consistent dynamical description. To this aim, within the RITMARE National Flagship Project, a specific research line on “Coastal Vulnerability to Erosion and Relative Sea level rise in climate change scenarios” was activated with reference to the Adriatic-Ionian region (Eastern Mediterranean Sea). The activities, supported by the Italian Ministry of University and Research 2016-18, move along three interconnected branches, namely: 1) Assessment of vulnerability to relative sea level rise in the Adriatic-Ionian region, in present conditions and in different climate change scenarios; 2) Development of high-resolution oceanographic modelling tools for the description of meteo-marine climate and sediment transport at different scales and rapid response intervention protocols for the evaluation of the impact of erosive events on sandy sediments; 3) Identification of possible geomorphological setting scenarios and definition of intervention strategies, with special care to the exploitment of marine sand as a strategic resource. The work provides an overview of the strategy underlying the Research Line and present preliminary results and main achievements. Next steps will be aiming to pave the way towards a road map for an integrated observational and modelling approach for monitoring and managing the erosion and marine ingression risk throughout Italian coasts, striving to bridge the cultural and methodological gaps between the scientific and administrative sectors active in the coastal management field.

Il ciclone Mediterraneo sviluppatosi tra il 7 - 8 novembre 2014 a nord della costa Libica ha manifestato intensità e caratteristiche tipiche di un ciclone tropicale e ha interessato direttamente nel suo spostamento verso est sia l'isola di Malta che la costa orientale della Sicilia. Le simulazioni effettuate con i modelli BOLAM e MOLOCH ed il confronto con le osservazioni disponibili hanno permesso di descriverne le caratteristiche nelle diverse fasi di sviluppo e, in particolare, di evidenziare la bassa predicibilità della peculiare traiettoria seguita dal ciclone, come mostrato anche dalle previsioni dei principali modelli globali e da altri modelli a mesoscala ad alta risoluzione. Per questi ultimi, oltre alla notevole incertezza nell'analisi (condizione iniziale), anche le condizioni al contorno ai bordi del dominio di integrazione hanno esercitato un notevole impatto sulle simulazioni modellistiche. Attraverso esperimenti numerici, si è cercato di investigare e distinguere il ruolo della circolazione a larga scala (onda baroclina) in cui il ciclone si sviluppa e il ruolo della circolazione in prossimità del ciclone stesso. Per quanto non sia stato possibile separare in modo chiaro i due contributi, risulta che la forzante a larga scala assume un ruolo decisamente importante nel guidare lo spostamento dell'intenso ciclone.

During the first HyMeX Special Observation Period (SOP1) field campaign, the target site of north‐eastern Italy (NEI) experienced a large amount of precipitation, locally exceeding the climatological values and distributed among several heavy‐rainfall episodes. In particular, two events that occurred during the last period of the campaign drew our attention. These events had common large‐scale patterns and a similar mesoscale setting, characterised by southerly low‐level flow interacting with the Alpine orography, but the precipitation distribution was very different. During Intensive Observing Period IOP18 (31 October–1 November 2012), convective systems were responsible for intense rainfall mainly located over a flat area of the eastern Po Valley, well upstream of the orography. Conversely, during IOP19 (4/5 November 2012), heavy precipitation affected only the Alpine area. In addition to IOP18 and IOP19, the present study analyses other heavy‐precipitation episodes that display similar characteristics and which occurred over NEI during the autumn of recent years. A high‐resolution (2 km grid spacing) non‐hydrostatic NWP model and available observations are used for this purpose.\ud \ud The two different observed precipitation patterns are explained in terms of interaction between the impinging flow and the Alps. Depending on the thermodynamic profile, convection can be triggered when the impinging flow is forced to rise over a pre‐existing cold‐air layer at the base of the orography. In this situation a persistent blocked‐flow condition and upstream convergence are responsible for heavy rain localized over the plain. Conversely, if convection does not develop, flow‐over conditions are established and heavy rain affects the Alps. Numerical parameters proposed in the literature are used to support the analysis.\ud \ud Finally, the role of evaporative cooling beneath the convective systems is evaluated. It turns out that the stationarity of the systems upstream of the Alps is mainly attributable to persistent blocked‐flow conditions, while convective outflow slightly modifies the location of precipitation.

During Intensive Observation Period 13 (15 to 16 October 2012) of the first Special Observing Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX), Southern Italy (SI) was affected by two consecutive heavy precipitation events (HPEs). Both HPEs were associated with multi-cell V-shaped retrograde regeneration mesoscale convective systems (MCSs). The life cycle of two MCSs in connection with their dynamic and thermodynamic environments were analysed using a combination of ground-based, airborne and spaceborne observations and numerical simulations. Rain gauges revealed that heavy precipitation occurred in two phases: the first one from 1300 to 1700 UTC (35 mm h-1) was caused by a V-shaped system initiating over the Tyrrhenian Sea in the early morning of 15 October. Convection was triggered by the low-level convergence between the southwesterlies ahead of an upper-level trough positioned over southeastern France and very moist southerlies from the Strait of Sicily. The convection was favoured by high convective available potential energy (1500 J kg-1) resulting from warm and moist conditions at low levels associated with high sea surface temperatures in the Strait of Sicily. In addition, humidity at mid-level was enriched by the presence of an elevated moisture plume from tropical Africa, favouring the efficiency of the convection to produce more precipitation. The second phase of heavy precipitation (2300 UTC on 15 October to 0200 UTC on 16 October, 34 mm h-1) was caused by a MCS initiating over Algeria around 1300 UTC, which subsequently travelled over the Strait of Sicily toward Sicily and SI. Convection was maintained by the combination of large low-level moisture contents and a marked convergence ahead of the cold front. Unlike other MCSs forming in the same region earlier on that day, this huge V-shaped system did affect SI because the strong upper-level flow progressively backed from southwesterly to south southwesterly.

High Impact Weather (HIW), particularly Heavy Precipitation Events (HPE), are common phenomena affecting the western Mediterranean (WMED) especially in the autumn period. Understanding and evaluating the capability to adequately represent such events in model simulations is one of the main goals of the Hydrological cycle in the Mediterranean Experiment (HyMeX) and the main motivation of this investigation. In order to gain a better knowledge of the model representation of HPE and related processes we perform a seamless multi-model intercomparison at the event scale. Limited-area model runs (grid spacing from 2 to 20km) at weather and climate time-scales are considered, four with parametrized and five with explicit convection. The performance of the nine models is compared by analysing precipitation, as well as convection-relevant parameters. An Intensive Observation Period (IOP12) from the HyMeX-SOP1 (Special Observation Period) is used to illustrate the results. During IOP12, HPE affected the northwestern Mediterranean region, from Spain to Italy, as a consequence of Mesoscale Convective Systems (MCSs) which initiated and intensified in the area of investigation. Results show that: (i) the timing of the maximum precipitation seems to be linked to the representation of large-scale conditions rather than differences among models; (ii) Convection Permitting Models (CPMs) exhibit differences among each other, but better represent the short-intense convective events. All four convection-parametrized models produce a large number of weak and long-lasting events. Regional Climate Models (RCMs) capture the occurrence of the event but produce notably lower precipitation amounts and hourly intensities than CPMs and Numerical Weather Prediction (NWP) models with parametrized convection; (iii) these differences do not seem to come from mean moisture or Convective Available Potential Energy (CAPE) which are in the same range for all models, but rather from differences in the variability and vertical distribution of moisture and the triggering of deep convection.

The Hydrological Cycle in the Mediterranean Experiment (HyMeX; Drobinski et al., 2014) is a 10-year (2010-2020) GEWEX Hydroclimatology Panel (GHP) Regional Hydroclimate Project (RHP). Its objectives are to: (i) improve the understanding of the water cycle, with emphasis on extreme events, by monitoring and modeling the Mediterranean coupled system (atmosphere-land-ocean), its variability (from the event scale to the seasonal and interannual scales) and characteristics over one decade in the context of global change; and (ii) evaluate societal and economical vulnerability, and adaptation capacity to extreme meteorological and climate events.