Agostino Manzato

The status and priorities of research on severe convective storms in Italy are outlined here, with particular attention to the upcoming Thunderstorm Intensification from Mountains to Plains (TIM) observation campaign. The increased intensity of events induced by climate change is attracting growing attention from the Italian scientific community on this topic. While northern Italy is the most studied, with numerous papers analyzing intense events such as tornadoes, hailstorms, and flash floods, there are still many open questions. The central and southern regions are less explored, even though they are also occasionally subject to intense events modulated by mesoscale circulations, sea-land interactions, and complex orography. The TIM campaign represents a unique opportunity to improve the understanding, monitoring, and forecasting of severe storms. The campaign, led by the European Severe Storm Laboratory, represents a first-of-this-kind pan-European campaign aimed at obtaining coordinated data on severe convective storms, and is a key step toward improving warnings, forecasts, climate change impact estimation, and adaptation measures. The value of the campaign for Italy is indicated by the participation of several institutions, both from the academic and the operational community. Among the planned initiatives, the use of two Italian airborne platforms will allow for a more complete characterization of the environments associated with convective storms, including an improvement in our understanding of the role of aerosols and storm-scale modeling.

The status and priorities of research on severe convective storms in Italy are outlined here, with particular attention to the upcoming Thunderstorm Intensification from Mountains to Plains (TIM) observation campaign. The increased intensity of events induced by climate change is attracting growing attention from the Italian scientific community on this topic. While northern Italy is the most studied, with numerous papers analyzing intense events such as tornadoes, hailstorms, and flash floods, the central and southern regions are less explored, even though they are also occasionally subject to intense events modulated by mesoscale circulations, sea-land interactions, and complex orography. The TIM campaign represents a unique opportunity to improve the understanding, monitoring, and forecasting of severe storms. The campaign, led by the European Severe Storm Laboratory, represents a first-of-this-kind pan-European campaign aimed at obtaining coordinated data on severe convective storms, and is a key step toward improving warnings, forecasts, climate change impact estimation, and adaptation measures. The value of the campaign for Italy is indicated by the participation of several institutions, both from the academic and the operational community. Among the planned initiatives, the use of two Italian airborne platforms will allow for a more complete characterization of the environments associated with convective storms, including an improvement in our understanding of the role of aerosols and storm-scale modeling.

The status and priorities of research on severe convective storms in Italy are outlined here, with particular attention to the upcoming Thunderstorm Intensification from Mountains to Plains (TIM) observation campaign. The increased intensity of events induced by climate change is attracting growing attention from the Italian scientific community on this topic. While northern Italy is the most studied, with numerous papers analyzing intense events such as tornadoes, hailstorms, and flash floods, the central and southern regions are less explored, even though they are also occasionally subject to intense events modulated by mesoscale circulations, sea-land interactions, and complex orography. The TIM campaign represents a unique opportunity to improve the understanding, monitoring, and forecasting of severe storms. The campaign, led by the European Severe Storm Laboratory, represents a first-of-this-kind pan-European campaign aimed at obtaining coordinated data on severe convective storms, and is a key step toward improving warnings, forecasts, climate change impact estimation, and adaptation measures. The value of the campaign for Italy is indicated by the participation of several institutions, both from the academic and the operational community. Among the planned initiatives, the use of two Italian airborne platforms will allow for a more complete characterization of the environments associated with convective storms, including an improvement in our understanding of the role of aerosols and storm-scale modeling.

The status and priorities of research on severe convective storms in Italy are outlined here, with particular attention to the upcoming Thunderstorm Intensification from Mountains to Plains (TIM) observation campaign. The increased intensity of events induced by climate change is attracting growing attention from the Italian scientific community on this topic. While northern Italy is the most studied, with numerous papers analyzing intense events such as tornadoes, hailstorms, and flash floods, the central and southern regions are less explored, even though they are also occasionally subject to intense events modulated by mesoscale circulations, sea-land interactions, and complex orography. The TIM campaign represents a unique opportunity to improve the understanding, monitoring, and forecasting of severe storms. The campaign, led by the European Severe Storm Laboratory, represents a first-of-this-kind pan-European campaign aimed at obtaining coordinated data on severe convective storms, and is a key step toward improving warnings, forecasts, climate change impact estimation, and adaptation measures. The value of the campaign for Italy is indicated by the participation of several institutions, both from the academic and the operational community. Among the planned initiatives, the use of two Italian airborne platforms will allow for a more complete characterization of the environments associated with convective storms, including an improvement in our understanding of the role of aerosols and storm-scale modeling.

In the early morning of 1 August 2021, a supercell developed over the Veneto plain and moved eastward towards Friuli-Venezia Giulia, locally producing hailstones with diameters up to 9 cm.In the present work, this event is studied by means of simulations with the Weather Research and Forecasting (WRF) model at 1 km resolution, coupled with the HAILCAST hail growth parameterization, which provides estimates of the maximum hail size at the ground. Several simulations are performed using different initial and boundary conditions (GFS and IFS forecasts), different initialization times and physics options, to study the predictability of the event.The analysis of the model results highlights a significant sensitivity to the forcing meteorological model and the initialization time. In particular, WRF is not able to properly simulate the development of strong convection over the Veneto and Friuli-Venezia Giulia plain in the early morning of 1 August using GFS forcing, while better results are obtained with IFS initial and boundary conditions, especially when simulations are initialized more than 24 hours before the event. Moreover, results are significantly affected by the microphysics scheme and the land surface model, while the planetary boundary layer parameterization seems to have a minor influence. However, the development of the supercell is properly simulated, with hailstone diameters comparable to observations, only when data from radiosoundings of Udine Rivolto are nudged into the model, highlighting the importance, and at the same time the complexity, of correctly reproducing local thermodynamic conditions for the simulation of extreme convection events.

Azzano Decimo, northeast Italy, was hit by major hail events in August 2021 and July 2023. The second event broke the European hail size record, whereas the first event led to nine 10-cm-sized hailstone samples that were preserved for subsequent examination. This essay presents the involvement of Osservatorio Meteorologico Regionale dell’Agenzia Regionale per la Protezione dell’Ambiente Friuli Venezia Giulia (OSMER–ARPA FVG)1 with both events, along with the meteorological and cultural backgrounds: Hail in Italy is far more frequent and severe than naïvely expected from a stereotype of Italy. The severeness of the hail in this area can even be felt vividly through the tradition of Italian music, especially in Summer of Vivaldi’s Four Seasons . Also touching on social–economical aspects, including various technologies used for hail prevention, this essay suggests how our history and culture can be deeply influenced by severe weather events.

On July 24, 2023, the new European record for hail size was set in northeast (NE) Italy with a 19‐cm wide hailstone recorded during a supercell outbreak. During this event, severe storms were triggered in the Alps, moved eastward, intensified rapidly in the foothills, and generated damaging hailstorms in the plains. A detailed analysis of the available observations and numerical simulations highlights that the atmospheric environment was unusual. A high‐ tongue over the Adriatic Sea was lifted by a southerly flow above the cold pool generated by the thunderstorm outflow associated with an initial supercell. This raised the most unstable layer to 1–2 km above mean sea level in the area affected by the record‐breaking hailstorm. The vertical profile was characterized by moderate potential instability (likely a value of fed the storms) and an intense southwesterly flow in the mid‐troposphere. Additionally, there was anomalously high water‐vapor transport in the layer 2–5 km above mean sea level. Consequently, high instability seems unnecessary for the occurrence of giant hailstorms in the region. This hypothesis is assessed with a statistical analysis performed for the 2018–2023 period in NE Italy using hail reports and observed soundings. The results show that hail size has a much lower correlation with potential instability compared with kinematic parameters of the mid‐troposphere and water‐vapor transport –. Furthermore, thermodynamic parameters have better skill in predicting the occurrence of hail or large hail , while kinematic parameters of the mid‐troposphere are better predictors for very large and giant hail events.

For climate models, forecasting environmental parameters has usually been easier than explicitly predicting storm activity, including lightning, hail at ground, and accumulated convective rainfall. It is common to identify—on past data—some statistical relationships between environmental parameters that favor storm occurrence or intensification and storm-related observations. Then, these relationships are applied to future model scenarios. In this study, many environmental parameters derived from radiosounding observations in northeastern Italy are studied during the 1992–2022 convective seasons (April–September), and their changes in this 31-yr period are assessed. For instance, the temperature (averaged across different mandatory levels) shows an increase of approximately 0.53°C every 10 years, while the precipitable water exhibits a positive trend of about 13% (1°C)⁻¹. Most of the examined indices, particularly those linked to water content and potential instability, are characterized by a noticeable upward trend that should potentially favor the storm formation and intensification. However, upon studying corresponding storm-related observations, similar trends do not clearly emerge. In fact, rain, lightning, and hail provide statistically nonsignificant trends. In conclusion, finding a statistical relationship between more favorable environmental parameters and the observed convective events is not straightforward. In fact, the development of storms is a highly complex phenomenon and simple statistical relationships with average environmental conditions could miss some of the underlying mechanisms. At the local scale of northeastern Italy, the relationships between environmental parameters and storm development are not climate change invariant. This sheds new light on the estimation of future storms in the perspective of global warming.

Temperature (T), pressure (p) and density (ρ) are the three fundamental variables that describe the local behaviour of the atmosphere through the ideal gas law. This work aims: 1) to investigate the mutual dependence of these variables near the Earth’s surface in the real-world atmosphere (i.e. not in idealized conditions); 2) to assess the physical conditions that lead to positive or negative correlations R(p,T). Possible applications of this study are: i) to improve the knowledge of the interdependence between meteorological variables at the local level, at least for the stations considered; ii) more in general, to classify stations objectively (e.g. dividing valley floor stations from top stations), according to the relationship between physical parameters; iii) identify implausible observations of meteorological variables. First of all, from hourly data it is found that temperature and pressure are weakly related if compared to density and temperature, which show a correlation close to 1. In fact, temperature and density depend only on local thermodynamic conditions, while pressure is representative of the properties of an entire vertical column of air. Moreover, from a temporal variation perspective, it is found that, on average, the normalized hourly change in pressure is very low with respect to temperature and density temporal variations. A second result we present is that scatterplots of hourly pressure versus temperature reveal a triangular shape for various stations we considered at different latitudes in extratropical areas. For all the locations it was always possible to fit the upper side of the triangle with a line of the same slope and with an intercept proportional to the mean pressure of the station. This suggests that a physical boundary exists in the extratropics, above which combinations of pressure and temperature cannot be observed. An exception are the high mountain stations, for which the scatterplots show a strong correlation very similar to what is found in the free atmosphere. Also the behaviour in the tropics is different, with a density-plot closer to a 2D gaussian distribution; however, the fitted line still represents an upper limit. Eventually, hourly data are aggregated at different temporal scales and correlations are computed: the analysis shows a hourly sinusoidal variation of the correlation R(p,T) during the day, reaching a maximum in the afternoon and a minimum in the night, that can be found in all the extratropical stations considered.