Tom,
What an excellent sequence!
Hmmmm.... 38 degrees, wet, open car without even so much as a windshield, snow/ice all over a Mustang in the paddock...
The only word that readily comes to mind is "certifiable".
If I remember right, aren't you running the Firehawks for rain/street tires? If so, I'd be reluctant to even call them "good" rain tires. I found them to be fair dry tires and that was about the extent of it. And I'm sure yours have been heat-cycled more than a couple times...
After having tried many different tires on the WRX and a couple on the STi, I'm quite fond of the Bridgestone Potenza RE070's. They're great in both rain and dry. Though as soon as my suspension's up to snuff, or at least I have caster plates, I'm moving to Hoosiers, which should yield sick lap times in the STi. Would expect that combo to make the STi a 1:45 car at MAM.