WATKINS GLEN, New York – The 30-minute race-morning practice typically held at Verizon IndyCar Series road- and street-course events likely took on its greatest significance of the season today at Watkins Glen International.

With light rain falling on a wet track, the 21 drivers entered in this afternoon’s INDYCAR Grand Prix at The Glen used the session to log invaluable laps on the Firestone wet-condition tires. With the forecast calling for an 80 percent chance of rain during the 60-lap race on the 3.37-mile, 11-turn permanent road circuit, the track time this morning was critical as teams worked on car setups for wet conditions.

INDYCAR GRAND PRIX AT THE GLEN: Warmup practice results; Combined practice results; Race tire designation

Dale Coyne Racing’s Sebastien Bourdais set the fastest lap, at 1 minute, 45.9510 seconds (114.506 mph) under drying track conditions before heavier rain began falling late in the session. For sake of comparison, Bourdais’ time in the No. 18 UNIFIN Honda was more than 23 seconds slower than Alexander Rossi’s pole-winning lap in dry conditions on Saturday.

“We didn’t get much water, so it was tough,” Bourdais said. “We blistered the tires early on when it was kind of dryish. I was happy that the car was still drivable when it got rainy a little bit more, but it was not massively wet.

“I really don’t know what’s going to happen if it does get really wet at any point,” added Bourdais, winner of the season-opening Firestone Grand Prix of St. Petersburg and in his second race back since recovering from injuries sustained in an Indianapolis 500 qualifications crash in May. “I think it’s a big curveball for everybody.”

Rossi was second with a lap of 1:45.9615 (114.494 mph) in the No. 98 NAPA Auto Parts/Curb Honda as each driver ran between seven and 13 laps in the warmup. Most stuck strictly to the rain tires but a few ventured on course on slick tires – including Andretti Autosport’s Marco Andretti and Ryan Hunter-Reay and AJ Foyt Racing’s Carlos Munoz.

Munoz logged the fourth-best lap on rain tires (1:46.1930, 114.245 mph) before swapping out for a set of Firestone alternate slicks. About the time he did, however, the rain picked up and Munoz had to gingerly nurse his No. 14 ABC Supply AJ Foyt Racing Chevrolet around the course and back to the pits.

Team Penske’s Josef Newgarden, the championship leader with two races remaining, was ninth in the warmup. Newgarden holds a 31-point lead over Chip Ganassi Racing’s Scott Dixon, who was 10th in the practice.

The current Firestone rain tire has yet to be used in a race, though it has seen sporadic use in wet conditions during practice sessions.

“We don’t know the tire, we’ve got no (race) experience here in the rain, so we’ll see,” Bourdais said. “It looked fairly competitive.

“We tried them once before in Barber warmup, I think. But the tire’s going to behave differently at every track, so it’s super difficult to really anticipate what the thing’s going to do, what you want tire pressure-wise. Just a lot of open questions but it’s the same for everybody.”

Each team must still declare what Firestone dry specification tire – primary black sidewall or alternate red sidewall – on which it will start the race if conditions are dry. If INDYCAR mandates a “wet” start for the race, all cars must be equipped with rain tires and the rule mandating each car use a set each of the primary and alternate dry tires in the race is waived.

Live race coverage begins at 1 p.m. ET on NBCSN and the Advance Auto Parts INDYCAR Radio Network.