Federico Grazzini

A workshop on high-impact meteorological events in Italy was jointly organized by the newly formed Italia Meteo Agency (AIM) and the Italian Association of Atmospheric Sciences and Meteorology (AISAM) on September 27, 2022. The aim of the workshop was to promote the sharing of the experiences that all operational and research meteorological centers in Italy have gained on specific types of high-impact events, favoring the establishment of a common know-how of Italian operational meteorology.

Numerical weather prediction models (NWP) are today the best suitable tools for temperature forecast. Nevertheless, raw model output is strongly affected by systematic errors, mostly due to the rough representation of orography; such errors can be partially corrected by Model Output Statistics techniques (MOS). In this study, aiming to operate frost alerting in Trentino, both linear and nonlinear MOS algorithms are compared in predicting minimum temperature in the middle Adige Valley area. Two NWP models have been used, one Global Circulation Model (ECMWF T511 - L60) and one Local Area Model (LAMI). The following post-processing techniques have been employed: mean bias correction, multilinear regression, neural networks, random forest (RF). The latter was selected as the best performing method, and applied to the nine points (for ECMWF) and to the 21 points (LAMI) surrounding the target area. Results show that multivariate models display the best skill, but with little difference am...

The summer 2002 will be remembered for the floods that devastated many parts of Central Europe. Early warnings 3 to 4 days in advance might have mitigated some of the devastations. Both synoptic and quantitative aspects of ECMWF deterministic and ensemble forecasts will be discussed. It will be shown that although some indication of large rainfall accumulation could be found

<p>Heavy precipitation events on the southern side of the Alps are typically associated with a favourable large-scale environment, characterized by an upper-level trough or cut-off cyclone over the western Mediterranean. This configuration induces, at the meso -scale, a meridional transport of large amount of moisture towards the orography, often organized in the form of a pre-frontal low-level jet. The thermodynamic characteristics of the impinging moist flow and its interaction with the orography determine the distribution and the intensity of the rainfall.</p> <p>The present study shows that, besides the local contribution from the Mediterranean Sea, a relevant amount of moisture may move from the tropics towards the Mediterranean within long and narrow filament-shaped structures, known as atmospheric rivers (AR). To this aim, a detection algorithm, designed for the open oceans, has been adapted to the peculiar morphology of the Mediterranean and applied to identify ARs during some of the most severe weather events affecting the Alpine region in the last decades. Moreover, some diagnostic tools, such as an algorithm for the calculation of the atmospheric water budget, have been employed to compare and investigate such AR events.</p> <p>The presence of ARs across the Mediterranean has been recently associated with heavy precipitation over southern Europe and Italy in particular. However, their role has not been fully assessed yet, in terms of contribution to the rainfall amount and of interaction with the cyclones driving their evolution. Therefore, high resolution numerical simulations are exploited to investigate how the transport of water vapour associated with the AR may have impacted on the severity and dynamics of a recent heavy precipitation event affecting the western Alps, and to disentangle how much rainfall can be attributed directly to the presence of the AR.</p>

<p>It is scientifically established that global warming induced by greenhouse gases, affecting the surface energy budget, can significantly alter the Earth's water cycle, with consequent modification of precipitation typology and regime. However, the net effects of these changes on the process of groundwater discharge are still uncertain at local scale. The lack of historical series of monitoring data, dating back to at least 60-100 years ago, is among the main drawbacks, with the rare exception of major karst springs exploited for public water supply. In hard rock aquifers, like those dominant in the Northern Apennines, the dynamic of spring outflow during the first half of the XX century is an absolute black-box. For this reason, it appeared noteworthy to analyze detailed monthly-based monitoring data, over the 1915-1920 time span, of the whole discharge of the Nadìa spring, one of the most productive spring in the Emilia-Romagna region, in low flow season, among those used for drinking water. Such data were reported in a century-old study functional to the drilling of a draining tunnel for water uptake. We present a comparison between the monthly regime of the spring discharge 100 years ago and a continuous monitoring performed by the authors during the 2020/2021 hydrological year, integrated with the total water uptaken in years 2018-2020. Nadìa spring discharges from an arenitic fractured aquifer deposited in a neritic setting above mainly clayey units acting as a permeability threshold. The abundance of calcite in the grains and cement of the arenite enhances corrosion and enlargement of fractures. In 2018-2021 the spring discharge range has been 80-50 L/s whereas in 1915-1920 it was 140-63 L/s. The two (ancient and recent) sets of data were compared with a focus on the evolution of precipitation, snow-fall and thermal regime.</p>

<p>Several studies on extreme precipitation events (EPEs) in the alpine area reported, as the main triggering factor, a meridionally elongated upper-level trough (i.e., a breaking Rossby wave) as part of an incoming Rossby wave packet (RWP). In this work, we investigate a vast number of EPEs occurring between 1979 and 2015 in northern-central Italy. The EPEs are subdivided into three categories (Cat1, Cat2, Cat3) according to thermodynamic conditions over the affected region. The three categories do not only differ locally but also in the evolution of precursor RWPs. These differences cannot be solely explained by the apparent seasonality of the flow; therefore, the relevant physical processes in the RWP propagation of each case are further investigated. In particular, we show that RWPs associated with the strongest EPEs, namely the ones falling in Cat2, undergo a substantial amplification over the western N. Atlantic due to anomalous ridge-building two days before the event; arguably due to diabatic heating sources. This type of development induces a downstream trough which is highly effective in focusing water vapour transport towards the main orographic barriers of the Apennines and the Alps. Finally, we identify an increasing trend of water vapour transport over the western N. Atlantic which is likely associated with the observed increase in Cat2 and Cat3 events</p>

An experimental 30-day weather forecasting system has been set up recently at ECMWF. This system is running twice a month, based on 51 coupled ocean-atmosphere integrations. Some of the products are based on weekly mean anomalies relative to model climatology of the past 12 years. The forecasts starting on 17 July 2002 display a significant anomaly of precipitation for weeks

<p>In a previous transfer project T1 of the SFB-Transregio “Waves to Weather” (W2W) a strategy was designed to classify precipitation extremes in Northern Italy and to provide additional information on the physical and dynamical drivers associated with it. Building on this, in collaboration with ARPAE-SIMC and ECMWF, we designed a new transfer project called TEX (Towards seamless prediction of EXtremes). The project has the final goal to expand and generalize this dynamical methodology to other regions and into the sub-seasonal forecast range (10-30 days). In this contribution, we present the first results concerning the validity of this method in the medium-range forecast. In particular, we show the accuracy of the random forest classification method, essentially based also on atmospheric upper-level predictors, in recognizing days with a high probability of extreme precipitation events compared to a forecast based only on precipitation outputs. These results, which are still referring to the test area of N-Italy, are preparatory for a further generalization to different areas and at a longer forecast horizon.</p>

Weather prediction is a fundamental scientific challenge and crucial to society. Predicting extreme weather events is one of the outstanding achievements of science. Despite the enormous progress made by modern meteorology, the precise prediction of certain critical phenomena, like extreme precipitation, can still be uncertain even at shorter time ranges. This research aims to identify the relevant atmospheric processes for the formation of extreme precipitation. We investigate the relationship between the predictable large-scale dynamics that create the right conditions for the genesis of extreme events, and fast small-scale processes, such as convection, which rapidly destroy predictability and pose a challenge for a correct forecast. In the aim to identify common dynamical states, we designed a systematic investigation on extreme precipitation events (EPEs), based on a very large number of episodes (> 800), which occurred between 1979 and 2015 in northern-central Italy, used a...

The manuscript by Ménégoz et al. investigates precipitation trends in the Alpine region through the aid of regional climate model MAR applied over the period 1903-2010. The model is forced by boundary condition from ERA-20C. Details of climate change over the Alps, especially for precipitations, need to be clarified further. Local feedbacks respect to air mass temperature increase, soil conditions, moisture availability also in relation with altitude in addition to changes in the dynamics of weather pattern are all factors potentially affecting precipitation distribution.

In 2015 an intense rainfall event hit the Valleys of the Trebbia, Nure, and Aveto watercourses in the Northern Apennines. In about 6 h a mesoscale convective system deployed a stunning amount of precipitation of 340 mm, with an extreme hourly rainfall intensity of >100 mm/h. It triggered debris flows along slopes and stream channels, landslides and floods, which caused serious damages. Through the optimal combination of rainfall data and radar volumes, in this work we present a detailed rainfall analysis, which will serve as a basis to create a quantitative correlation with debris flows over elementary hydrological units. We aim at providing an objective basis for future predictions, starting from the recognition of the forcing meteorological events, and then arriving at the prediction of triggering phenomena and to the debris-flow type. We further provide seven observations/case studies on the effects of extreme-precipitation events on freshwater environments in small mountain c...

... KATARZYNA STAROSTA 9 ... Wetterdienst, Offenbach, Germany 4Hellenic National Meteorological Service, Hellinikon, Greece 5National Meteorological Administration, Bucharest, Romania 6Agenzia Regionale per la Protezione Ambientale Emilia Romagna, Bologna, Italy ...

Extreme precipitation events (EPEs) are meteorological phenomena of major concern for the densely populated regions of northern and central Italy. Although statistically rare, they tend to be recurrent in autumn and share common characteristics in the large-scale dynamical evolution responsible for their generation. Past studies on EPEs have reported, as the main triggering factor, a meridionally elongated upper-level trough embedded in an incoming Rossby wave packet. In this respect, we show how the meteorological conditions leading to the devastating 1994 Piedmont flood represent a typical flow evolution for this type of extreme events. Exploiting the systematic classification of EPEs recently published by the authors and taking advantage of a new observational dataset, this article revisits the role of the large-scale flow on this and similar cases of past EPEs.

The steady improvement in resolution and realism of global models together with the arrival of ensemble techniques has meant that hints of severe weather can now be found as early as 3 to 5 days in advance in operational models. Examples will be shown of such cases. Systematic verification studies however rarely address such ranges. In this presentation, a new