|A broad ridge was present over Western Europe with hot and moist air near the surface, but Atlantic air was slowly moving in behind a decelerating cold front. Near and just ahead of this cold front isolated to scattered storms were expected to develop over Eastern Belgium, South-eastern Holland and Western Germany. Quite steep lapse rates in these areas were observed and in combination with observed 16 to 19 degrees dew points, more than 1000 J/kg MLCAPE should be able to form. As shear was rather weak, multicell storms were most likely.|
I left my home at about 13 LT and drove southeast. My car thermometer indicated rising temperatures and near Maastricht it was already 31°C. On the southern horizon I saw some Cumulus clouds starting to form, so I drove further south into Belgium. I found a rest area near Spa and here I observed convection for more than an hour. Towering Cumuli were present, often showing a pileus cloud, but they had troubles breaking the cap. Sometimes one succeeded, but pretty soon died because of drier air above the capping inversion. There was quite a lot of instability present as Cumulus growth could be seen with the naked eye. Ben Lankamp informed me about the situation by phone and it looked like I was in the right area. After a while I decided to drive off again, as a storm looked to be brewing to my southeast. Soon I saw an anvil, but it was ill-formed. Near the German border police set up a road block, but I could go on without much trouble. Unfortunately I got stuck in traffic soon there after and became frustrated as I saw the storm drift further east. It took at least half an hour to speed up again. Ben gave me another call and told me to go east...well that storm looked to be far away. I saw another tower growing rapidly to my northeast. According to Ben the storm was less active (about 50 dbz), but it was in reach. So I found my target and went in pursuit. It had a very active looking core and some sort of flanking line to its west. I went to the edge of the core and stopped at a rest area. Soon it started to hail! Hailstone size was roughly 0.5 to 1 cm. Also, some branches broke by wind gusts. I let the storm pass and headed northeast again, as new storms were forming in that direction. Sometimes a nice low base was visible and I even encountered some sort of LP'ish storm, but it wasn't rotating. It had a solid updraft, a nice anvil, but it hardly produced any rain. Herman informed me he was driving in my direction as well now.
At one moment it seemed storms were moving east too fast and with rush hour near the Ruhr area, I didn't think I would succeed catching up again. So I drove northwest, towards the Dutch border. At one moment I looked over my shoulder and saw an enormous storm with a gigantic overshooting top! Soon there after Ben called again and told me I should drive south again. I was in doubts, but did it anyway. I ended up between Köln and Koblenz again, chasing large towers and storms. Underneath the large anvil, mammatus clouds were present, but the setting sun was obscured by other storms, so contrast was poor. Lightning was great though, with CG's in the core and crawlers riding the anvil. At 22.30 LT I decided to call it a day and went home again.