Play was only possible before lunch at the Swalec Stadium, but during those 28 overs Glamorgan’s bowlers made inroads into Northamptonshire’s first innings.
When play was abandoned for the day the visitors were struggling at 79 for 5.
The rain threatened all morning and Glamorgan’s seamers took full advantage of cloudy skies and a green pitch to trouble the batsmen.
Resuming at 0-0, Stephen Peters and nightwatchman Mohammad Azharullah took the score to 28 for 0.
But then Northants collapsed 33 for 5, with five wickets falling for five runs in 35 balls.
Among those runs were five penalty runs, awarded when wicketkeeper Mark Wallace chased the ball to fine leg, returned to Colin Ingram who had by then put Wallace’s glove on to his hand - thus incurring the penalty.
Michael Hogan made the initial breakthrough when he uprooted Peters’ off stump with a ball that nipped back off the pitch.
He was quickly followed by Kyle Coetzer who chipped Hogan to midwicket.
There was no respite from the other Glamorgan seamers, with Craig Meschede inducing Rob Newton to edge one to Wallace.
Azharullah became Meschede’s second victim when he was well caught low down by Jacques Rudolph at slip who then took his second catch in Rory Smith’s first over.
Northants could have been in further trouble had Ben Wright, at midwicket, managed to hold on to a sharp chance offered by Josh Cobb before he had scored.
Cobb and Adam Rossington then counter-attacked effectively, with both batsmen hitting boundaries.
The County are still 143 runs away from the follow target of 222, but if Glamorgan’s bowlers can replicate their performance they will be confident of winning and gaining maximum points from the game.