This came across Casey’s Beach near Batehaven on the 5th January. The whole cloud mass came out of the south east and passed over in just 15 minutes. I estimated it to be 30-50 kilometers in length. You can’t see the end of it in this. It extended right out to sea into the dark area on the far right of the image. The whole cloud was rolling quite quickly, with the downdraft side closest and the updraft of course on the other side. Shot with a Canon G1X.