Each of the top three improved their times still further with their next lap, but it wasn't good enough to prevent Alex Tagliani jumping briefly into provisional pole with a lap of 1:176139s before Briscoe was able to responded with a 1:17.5177s.
Ryan Hunter-Reay ran a slightly contrary strategy by leaving it especially late to come out and start his run, but it worked beautifully and he was rewarded by a provisional pole time of 1:17.2338s on only his second effort with just 90s remaining in the ten minute session. Dario Franchitti came close to matching him and was just a hundredth of a second off with his best lap, before then running off at turn 1 as the rain started to pick up again in that part of the course.
Hunter-Reay is recorded as the polewinner and has a bonus championship point and a $10,000 oversized cheque to prove as much, putting an end to Franchitti's run of three consecutive official pole positions; but it's the Scot who will nonetheless lead the field to green alongside Ryan Briscoe on Sunday because of Hunter-Reay's ten-place staring grid penalty for an unscheduled engine change post-Toronto.
Most weather forecasts have been promising a dry race day, but a worrying trend has seen increasing chances of more showers start to factor in to the outlook for the Sunday race that gets underway at 12:45pm local time (7.45pm BST, shown live in the UK on Sky Sports
Full qualifying times
and unofficial provisional starting grid available.