wind, cold pools, and the Miller Park Crane accident

Just last night I saw a program on the Discovery Channel about the July 14, 1999 crane accident at Milwaukee’s Miller Park (then under construction). The accident was supposed to have been caused by a sudden increase in wind speed, and intrigued, I took a look at the archived ETA data at NOAA’s READY site to see what might have caused a sudden increase in wind. I now have a hunch and would like to bounce it off anyone else that might be interested.

Near the time of the accident early in the evening, The ETA output shows a large area of 15+ Knot surface winds out of the south across much of the Upper Midwest, with winds near 30 Knots near the top of the mixed layer. Milwaukee appeared to be just inside the southern margin of these winds at the time of the accident. The program mentioned that bad weather delayed operations earlier in the day.

My hunch is that the earlier showers or thunderstorms laid down a cold pool over the area and that this cold pool and its topping inversion prevented the mixing of the stronger winds downward for a few hours after the weather cleared, giving the false impression of benign conditions when regional synoptic scale winds were brisk (except in the cold pool). I suspect that the cold pool was finally “mixed outâ€￾ by daytime heating, or advected northward out the area, suddenly allowing the brisk winds to reach the ground, catching the crane operators by surprise and causing the accident.

Any thoughts about this hunch would be appreciated.