Application of a simple analytical model to severe winds produced by a bow echo like storm in northeast Italy

Abstract

A strong mesoscale convective system affected northeastern Italy on August 8, 2008. Notable damage and two casualties resulted, mainly due to the strong wind gusts. The event is analysed using observations, including surface data from a meso‐network of meteorological stations, radar reflectivity and velocity data from a C‐band Doppler radar, polar satellite images, lightning measurements from a lightning detection network and the ambient thermodynamic conditions derived from local radiosoundings. The role of the cold front is investigated; in particular, the associated strong wind descending from the Alps, which interacted with the preexisting convection in the plain, is analysed to understand the way it affected the storm development. A simple density current model is applied to describe the flow characteristics and to identify the mechanisms that could support the development of such a high wind speed. Lastly, observed wind speeds are compared with the theoretical estimates from the proposed model. The results show that different factors contribute to the very strong wind gusts registered by surface stations. The main contributor to the windstorm is a density current (a) driven by the cold front, (b) maintained by the interaction between the cold air impinging on the Friuli Venezia Giulia plain from the north and the strong regional density gradient and (c) eventually enhanced by the storm cold pool. This study highlights the complex evolution of severe storms in a region on the lee side of the Alpine chain, and emphasizes the role of the orography in the enhancement of storm.

Dynamical forcings in heavy precipitation events over Italy: lessons from the HyMeX SOP1 campaign

“…5), in agreement with the expected theoretical evolution of an extensive downburst into a bow-echo-like structure (Fujita, 1978). Similar evolutions over the area, in particular over the Grado Lagoon, sustained by strong cold air rear inflow, have been recently reported in other episodes of severe convection in the region (Pucillo et al, 2020). Hence, the latter emerges as a common mechanism for the intensification of deep convection, occurring when the warm and moist air near the Venice lagoon and the northern Adriatic Sea contrasts with cooler air behind a small cold frontal system moving eastward.…”

“…Therefore, most of the research efforts in HyMeX was devoted to attain a better understanding of convective episodes in order to finally improve forecast accuracy, or at least to increase awareness of the processes that anticipate the possible development of severe weather systems. In this framework, the Friuli Venezia Giulia (FVG) region is a suitable natural laboratory, since it does not only display the highest peak in the average yearly rainfall in the Alpine region (Isotta et al, 2014), but also a high frequency of severe convective episodes as thunderstorms (Feudale and Manzato, 2014;Pucillo et al, 2020), hailstorms (Manzato, 2012;Punge et al, 2014), tornadoes and waterspouts (Giaiotti et al, 2007), and bow-echoes (Pucillo and Manzato, 2010).…”

Observational analysis and simulations of a severe hailstorm in northeastern Italy

“…During the first phase, the West cell exhibits some features typical of a supercell, such as relatively large hail and the presence of a mesocyclone (or at least of a strong low-level convergence), as will be shown later. Dennis and Kumjian (2017) highlighted the important role of mesocyclones in hail growth, while Wapler 9 The smaller extension of the bow-echo features in this region was recently discussed by Pucillo et al (2020).…”

“…The particular exposure of FVG to severe weather is very likely related to its topography, which is confined between the Adriatic Sea to the south and the Alps to the north, with peaks that reach 2,780 m amsl. In particular, the northern Adriatic Sea and its lagoons are sources of moist and warm air, while the Alpine orographic barrier often helps to trigger thunderstorms (Houze, 2015;Davolio et al, 2016;Miglietta et al,2016;Pucillo et al, 2020).…”

Cold Pool Responses to Changes in Soil Moisture

“…That is, , where g denotes acceleration due to gravity, the overbar represents the base state, and the prime represents a deviation from the base state, is replaced by, essentially, (see Equation 6 of Schlemmer & Hohenegger, 2014). Pucillo et al (2020) take a similar approach.…”