Nico Rosberg made it two out of two in Austrian GP practice but heavy rain 10 minutes into the afternoon session severely disrupted proceedings.
The championship leader, who broke the Red Bull Ring record in Practice One, lapped the 2.6-mile track in a 1:07.967 in P2 before the showers began, just 0.019s faster than Lewis Hamilton as his team-mate made a late push on the ultrasoft tyres.
Nico Hulkenberg was some six tenths further back in third while Sebastian Vettel and Daniel Ricciardo followed the Force India in Spielberg. Vettel was later involved in the biggest spin of the session, dropping his Ferrari into the gravel after a bizarre lock-up.
Teams rushed cars out of the garage at the start of P2 with storm clouds looming over the circuit but drivers were reporting spots of rain on their visors within minutes.
Hamilton: Down to me to catch up
A downpour followed and Jolyon Palmer, Sergio Perez and Jenson Button were all victims of not being able to enter the pits in time, with Sky F1's Anthony Davidson comparing using slicks in the wet to "walking on ice".
Torrential rain and streams on the main straight saw the session halted for more than half an hour, with Daniel Ricciardo and Max Verstappen the first to return on the intermediate tyre for Red Bull.
But the track was too wet for the compound in some parts of the track and too dry in others and it took some time until softer rubber was able to be used once again.
With rain a strong possibility on both Saturday and Sunday most teams saw the conditions as good preparation for the weekend ahead, though Fernando Alonso told his team "I've not been learning anything for the last half hour", when asked if he wanted to return to the pits. Interestingly, Carlos Sainz set the pace on the intermediate tyre.
When the track was ready for slicks, Hamilton led a late charge while Rosberg focused on longer runs, but the world champion's best effort couldn't quite push his Mercedes team-mate off the top of the timesheets.
Drama at the end of Friday's running came from Ferrari, however, with Vettel pitched straight into the gravel when braking on the run-up to Turn Two.
"We had an issue with the brake distribution," Vettel told Sky Sports F1. "It caught me by surprise but it didn't matter too much and fortunately nothing happened."
Practice Two timesheet
1. Nico Rosberg, Mercedes, 1:07.967
2. Lewis Hamilton, Mercedes, 1:07.986
3. Nico Hulkenberg, Force India, 1:08.580
4. Sebastian Vettel, Ferrari, 1:08.589
5. Daniel Ricciardo, Red Bull, 1:08.649
6. Carlos Sainz, Toro Rosso, 1:08.713
7. Max Verstappen, Red Bull, 1:08.761
8. Kimi Raikkonen, Ferrari, 1:08.820
9. Valtteri Bottas, Williams, 1:08.941
10. Jenson Button, McLaren, 1:08.994
11. Fernando Alonso, McLaren, 1:09.075
12. Felipe Massa, Williams, 1:09.184
13. Daniel Kvyat, Toro Rosso, 1:09.207
14. Sergio Perez, Force India, 1:09.226
15. Kevin Magnussen, Renault, 1:09.525
16. Jolyon Palmer, Renault, 1:10.020
17. Pascal Wehrlein, Manor, 1:10.034
18. Esteban Gutierrez, Haas, 1:10.138
19. Marcus Ericsson, Sauber, 1:10.140
20. Romain Grosjean, Haas, 1:10.400
21. Felipe Nasr, Sauber, 1:10.444
22. Rio Haryanto, Manor, 1:11.328