Termas de Ro Hondo - World champion Marc Marquez shrugged off the showers to set the best time in Friday practice for the Argentina MotoGP.
The 25-year-old Spaniard dominated at the circuit des Thermes de Rio Hondo with a time of 1:39.395 on his Honda.
"It was a good day for us. When we started this morning, the track was quite slippery and we struggled a bit but it was the same for every rider, and the asphalt steadily became cleaner," said Marquez.
"In the afternoon, the second session was a bit strange as conditions were kind of mixed, but all in all we were able to do good work on the bike setup, getting a pretty clear idea about those conditions."
Fellow Honda riders Cal Crutchlow and teammate Dani Pedrosa were second and third fastest at 0.404 sec and 0.908 sec respectively.
Valentino Rossi, the 39-year-old nine-time world champion, managed only the seventh best time on his Yamaha at 1.182sec off the pace, one spot behind teammate Maverick Vinales.
"The main target was to stay inside the top 10, because the weather is very difficult to predict - this is very important," said Rossi.
Ducati's Andrea Dovizioso, the winner of the season-opener in Qatar last month, was a modest 15th with former world champion Jorge Lorenzo, also on a Ducati, was 16th.
1. Marc Marquez (ESP/Honda) 1:39.395, 2. Cal Crutchlow (GBR/LCR Honda) at 0.404, 3. Dani Pedrosa (ESP/Honda) 0.908, 4. Tito Rabat (ESP/RAR Ducati) 0.951, 5. Andrea Iannone (ITA/Suzuki) 0.991, 6. Maverick Vinales (ESP/Yamaha) 1.115, 7. Valentino Rossi (ITA/Yamaha) 1.182, 8. Alex Rins (ESP/Suzuki) 1.197, 9. Johann Zarco (FRA/Yamaha Tech3) 1.219, 10. Jack Miller (AUS/APR Ducati) 1.320
15. Andrea Dovizioso (ITA/Ducati) 1.543, 16. Jorge Lorenzo (ESP/Ducati) 1.624