The threat of rain meant that all 26 cars went straight out at the green light on a virtually-dry track using the Pirelli medium-compound tyres.
A flurry of fast times soon followed, with Felipe Nasr and Sam Bird the early pacesetters before Ericsson produced his 1m40.716s.
That would remain as the pole time, with rain spots finally arriving as cars headed pitwards for their second set of tyres.
When they re-emerged, the conditions were markedly worse and remained so until the end of the qualifying period.
Bird's Russian Time machine will start alongside Ericsson on the front row, his best time 0.371s slower than the Swede. Nasr will start third, with points leader Stefano Coletti alongside.
Coletti had a scare this morning, when he was slowest in free practice, but clearly regained his mojo in qualifying with fourth position.
Ericsson's team-mate Stephane Richelmi was fifth fastest, ahead of last year's Silverstone pacesetter Fabio Leimer.
Rio Haryanto and Mitch Evans were next up, ahead of Tom Dillmann and James Calado.
Those who failed to get a quick time in before the rain included Robin Frijns (who was quickest early on but will start 16th), Johnny Cecotto Jr (who spun on his out lap and will start 18th), Alexander Rossi (19th) and Jolyon Palmer (20th).
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- Felipe Nasr