Day 15 - In The Thick Of It

18 June 2010

We awoke in our nice motel, nice except for the English kids outside playing with a noisy dog. We did some number crunching and had to spend a little time deciding on a plan. The ever talented Storm Prediction Centre forecasters were pointing their highest tornado probabilities in Wisconsin, but the setup looked severe and Wisconsin is difficult chase territory. The road networks are ok but there are far more trees than most of the plains, making it difficult to see the lower levels of the storms. The day 2 outlook was looking better for Kansas and Nebraska and we, and some of our friends, were thinking the setup around the Minnesota / Iowa / Kansas border areas were looking pretty good. We set off for Des Moines, with another fairly long drive ahead of us. Our confidence grew in our choice as more chasers seemed to be choosing that area, and the storms in Wisconsin kicked off very early, looking big already.The storms, whether north or south, would again be initiated by lift from colder air. There was plenty of heat and water in the atmosphere, as was very apparent from the oppressive humidity. In the more stable weather systems of England, we certainly wouldn't expect such humidity so soon after such huge storms. Today's cold air wouldn't just be associated with cold and warm fronts, it would involve the cold air that is still emanating from yesterday's storms. It can be hard to conceptualise - these storms can grow so large and violent, that the air they push away from them actually creates new mesoscale (between about 50 and 2000 kilometres in size) weather systems. We've seen a fair amount of this type of interaction, it seems that once you've had one such system, the chances of more spawning from it increase. But to visualise a thunderstorm's cold outflow as something that will create clouds hundreds of miles away is one of the many things that adds complexity to trying to understand these systems.As we reached Des Moines the first storms in the southern target region kicked off. It was satisfying to realise we were going to be involved in some good weather without strictly following the SPCs outlooks! As we ploughed on past Des Moines a few cells were kicking off to our west and more were forming behind them. We decided to skip the first batch, which were growing in size and moving together, while the newer ones were staying a little more discrete. Even when the Des Moines storms started to show signs of rotation we persisted on our target. They actually did put down a tornado, sadly it was in Des Moines itself, causing some nasty damage.We raced down and got into position on our storm, we got into a good place, just as it started to show signs of rotation. It was a fairly well organised one, with new storms forming up behind it. It was great to be in the right place at the right time, for once!The storm continued to show some good signs, and we positioned, and repositioned to get to the right place to see anything happen, if it were going to, getting some more nice views of storm structure.

SPC Day 1 Weather Outlook as at 06:00UTC (01:00 Central Time the night before)

SPC 01:00UTC day 1 forecast for Fri June 2010

SPC Day 1 Weather Reports for the day.

SPC storm reports for Fri June 2010

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