Sevegliano (FVG) HP supercell, Sept 10, 2013

Day 3 of the active pattern. Still under a strong mid-level jet with 50 kt 500 mbar winds and another shortwave passing through, creating a very favourable low level wind pattern with strong backing surface winds. With SST still around 23-24 °C there was strong WAA in the Friuli and Veneto plains. Temperatures hovered around 23-25 °C, while dewpoints were also in the low 20ies! The WAA caused strong CAPE builtdup in the afternoon, evening and night hours with values up to 2000 J/kg.

This would be my third consecutive chase in this area in as many days. The mid afternoon hours already saw some minor supercells developing across the plain with several being caught by Nejc Ucman and Marko Korošec, who caught a very impressive small classic supercell near Cormons in eastern Friuli. This supercell was my first target of the day. Being late I opted for the route past Nova Gorica, hoping to intercept it head on, but I was too late. I saw the remnants of the supercell skirting the Goriška Brda hills to the north. Somewhat discouraged I continued southwestward to Villese, monitoring the developing activity in the eastern Veneto plains.

At about 20h local a rapidly organizing cluster formed SW of Portogruaro. It soon organized in a single isolated supercell. I exited the maze of local roads near Porpetto, where I found a local road with a couple of spots with a very clear view all around. Soon I spotted – in the near-constant CG and CC barrage – an outline in the west: low base, shelf cloud and inflow tail.

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The view was soon obscured by low clouds and rain, so I moved eastwards. Close to Sevegliano I spotted the impressive strom structure in my rear view mirror during a lightning strike. I pulled over next to an orchard and immediately a spectacularly structured mesocyclone and shelf cloud was visible.

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The structure was absolutely spectacular and 1.3-sec exposures (not illuminated by lightning) were blurred by motion and rotation of the supercell! The HP structure was very impressive: the shelf cloud was nearly on the ground, the wall cloud was nearly completely rain-wrapped with only a vague outline visible through the precipitation. A long inflow tail partially developed for a couple of minutes, with a broken chain of inflow clouds streaming into the wall cloud in the ~50 km/h sustained inflow. This was some of the best HP supercell structure I’ve ever seen.

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I then moved eastward, but my chase was interrupted by unmarked road construction works. The RFD precipitation caught me and it was impossible to get in front of the storm again. I then drove through much precipitation until Trieste, where I met up with Marko Korošec again. We watched a couple of smaller thunderstorms, though no supercells.

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