Viktor Östberg has topped a session for the first time in his career after making the best of the atrocious conditions during practice at Indianapolis to end up just under half a tenth ahead of Klaas van Snelheid.
The session was wet from start to finish with drivers never departing from the full wet tyres, though a small break in the consistent downpour during the middle of the session allowed a flurry of improvements for those who were on track at the right time before conditions worsened once more.
That left Östberg and van Snelheid some 1.2 seconds clear of third placed Olen Inman, while Thierry Xylander showed strong once again in his second outing of the season - this time in Allar Kangur's car - with fourth fastest, but more impressively keeping the car on track. Judson Sikes lapped fifth fastest ahead of Tumo Kinnumen, Carson Davenport and Enrique Ruiz, while a great lap from Finn Schnyder put the AMR driver into the top nine, ahead of the second Phoenix of Sergio Álvarez.
As a result of the conditions there were unsurprisingly a number of incidents - including two red flags - one of which was for championship contender Nathaniel Powers, who beached the car in the gravel on the outside of turn 3. The other was for Ryota Yoshida towards the end of the session as he lost the car exiting the final corner and slammed the inside barrier, ending a miserable day for Ocelot that saw Yoshida 20th and Puccio Giodano 22nd.
Rain is expected once again tomorrow for qualifying but to a much lesser degree, however it will still be a crucial session in which drivers will need to be on track and on the right tyre at the right time.
See below for full practice classification: