Taken just before embarking on the 'pirate boat' (the brown one in front of the white cruiser) to go a couple of miles along the coast from Portoroz to Piran, just south of Trieste.
The shelf cloud is directly above, the main thunderstorm cell is off to the right. I knew the trip was going to be rough with this set-up; if I'd realised how rough, I'd have stayed on shore!
About 10 minutes later, the storm hit us, with 2cm dia hailstones, the awnings round the sides of the boat splitting, and gusts sufficient to heel the boat over such that the entry port (level with the quayside in the photo) was dipping under water. I'd estimate the gusts at 100km/hr plus. Sorry no photos of the storm in action - too busy trying to keep dry, and to locate the life belts in case it came to that.
Within half an hour the storm had cleared, and the sun was out. But with the group on the boat having average age 75 or so (a Saga holiday) I wouldn't have given much for our various chances of survival if we had shipped a lot of water; it only just missed being a major tragedy.
A great capture! Shelf clouds, while they can make for dangerous conditions, are awesome things to look at. I truly cannot remember the last time I got to see one of those (apart from weak ones from decaying cold fronts).
Yes, great picture - and scary story to go with it.