Vivaro (FVG) tornadic supercell, May 11, 2014

May 11 saw a potentially explosive tornadic setup developing over the plains of Veneto and Friuli. Moderate instability of 1000 J/kg MLCAPE overlapped with a very impressively sheared environment. A 50 kt 500 mbar westerly jet was present ahead of the cold front, with a strong 20-30 kt SE-E surface jet developing across the Veneto and Friuli plains in the afternoon. The total DLS reached 60-70 kt and increased to 90 kt later in the afternoon with the front. SREH3 was 400-500 m2/s2. Any thunderstorm forming in these conditions had significant potential to become a tornadic supercell.

Prefrontal initiation began at 15h with a number of intense, but brief showers developing across the plain. Figuring any of the rapidly developing storms had the potential to become significant I headed towards intercept immediately. After two hours and two intercepts that produced nothing really noteworthy I met up with Marko Korošec and Andrea Troisi in San Vito al Tagliamento. A new cell developed to our northwest producing a nice rain-free base. We moved to intercept it near Valvason as it gained some organization, but refused to mature into a supercell.

Finally, a stronger cell began developing further west and we repositioned to about 3 km west of Vivaro. Coming around the FFD precipitation we were greeted by a rapidly developing supercell. The mesocyclone soon began developing some striation and inflow banding and fast rotation.

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Soon the RFD began cutting into the mesocyclone. Two areas of circulation developed. A small, but rapid circulation formed on the west side and the main mesocyclone on the east. The western circulation developed a brief small funnel cloud before occluding. The main mesocyclone further intensified and formed a brief cone funnel cloud.

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RFD continued to cut further into the mesocyclone, tightening up the rapid circulation in the wall cloud further.

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Soon the RFD cut was really spectacular. The rapidly rotating wall cloud was 2/3 of the way to the ground and picking up scud from ground level. We thought it might drop a tornado any second.

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These shots were done either at 24 mm on full frame or 10 mm on DX sensors, so the field of view is large. It does not do justice to the true size of the wall cloud. Below is a video grab made at 17 mm on APS-C, it gives a slightly better impression of how large it was.

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The wall cloud then soon occluded and we progressed further east, as the cell began a new cycle. The rest of the chase was spent in a rush, pushing to stay ahead of the rapidly moving storm. Not far ahead, while racing forward to get clear of the RFD precipitation I got hit by rapidly moving rain curtains, moving out of the storm, but then reversing direction into the storm within seconds. It turns out the cell went into another cycle of rapid tornadogenesis and I was grazed by the outer circulation of the Dignano tornado. Moving about 500 m further northeast I stopped, looking ahead into the new massive wall cloud which already had a big RFD cut forming. Meanwhile the tornado, now a big cone, was off to my left and I was still unaware of it. Marko and Andrea noticed it at about this time.

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Racing about a km further east I rejoined them. They had been watching the tornado for the past several minutes. Got a good look at it while it was still on the ground, but began roping out as I went to grab my camera. By that time, the tornado had been on the ground for at least 3 minutes.

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 We immediately resumed racing ahead as the aforementioned wall cloud began tightening up and a new rapid circulation developed on the back end of it.  We stayed with it for a couple of minutes, but it soon occluded as the storm began lining out. A new tail end Charlie storm began developing to the SW, south of Pordenone and we headed for intercept just W of Codroipo.

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While no particularly impressive storm structure was seen, a lowering / wall cloud on the tail end cell caught our attention. Not noticing it at that moment, a dark silhouette is visible in the rain curtains. Another tornado? No other reports have surfaced, so it is uncertain.  Should have used a tripod here, but this was a handheld shot at ISO 1600, so noise is quite abundant. The frontal push began soon after and the storms began lining out into a squall line, pushing across the Veneto / FVG plains into the north Adriatic.

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