It might have come at a good time for world No.1 Scottie Scheffler, who was making quite a charge until two bogeys in three holes, the last one from an iron off the tee into a creek.
And it probably won't help the players like Poston who face a long Sunday to make up for the lost time and then face playing 36 holes of US Open qualifying on Monday.
Poston and Gerard were tied at nine-under par through five holes, one shot ahead of fellow American Sam Burns, who was through six holes.
Only 21 players finished the round, with Harris English (69) posting the best score at 3-under 213.
Adam Scott, the lone Australian to survive the halfway cut, was tied 32nd at three over after playing 16 holes in one over, including two double bogeys.
Even with four hours of daylight available, the PGA Tour felt there was enough thunderstorm activity on the way to call it a day.
Scheffler, trying to join Tiger Woods as the only players to win three in a row at the Jack Nicklaus-hosted Memorial, started 10 shots behind and bogeyed the first hole.
And then in a matter of minutes, or so it seems with Scheffler, he was in fourth place after a birdie-birdie-eagle stretch approaching the turn, and then an 8-foot birdie to start the back nine.
But then he had a three-putt par from some 65 feet, back to front, on the par-5 11th. He found a back bunker on the par-3 12th, a spot where it's nigh impossible to keep it on the green (he didn't) leading to another bogey.
And then on the 14th, his iron drifted left and led to a splash and a penalty stroke, adding to a bogey that dropped the world's No.1 player to 2 under for the round at tied 12th, still eight shots behind.
This was no longer the same Muirfield Village, fast and firm and frightening all week, suddenly softened by bursts of rain and even some hail.
No one felt it quite like Justin Thomas, who had made a superb par save from behind the 18th green on Friday to make the cut on the number.
He only played 12 holes in dry conditions before the first delay of one hour, 40 minutes. Enough rain fell to make the course a touch easier. And now 32 players still on the course return to a course much softer and easier.
Thomas could only chuckle at his bad luck after his round of 72.
"That's kind of the joy of being first off because you normally get no wind and an easier course," he said. "But I missed the window. You know, you've got to play better."
