Parnell, on his Northants debut, and the rest of bowlers suffered a testing opening day to their LV= Insurance County Championship Group 3 clash.
After winning the toss and bowling on a beautifully sunny day, the County battled hard with the ball but the Welshmen had reached 324 for seven at the close, with Chris Cooke unbeaten on 107.
Gareth Berg was the pick of the attack taking three for 52 from 19 overs, while there were two wickets in two balls for Saif Zaib (2-32) and also a pair of scalps for Parnell who ended with two for 66 from 18 overs.
“It has been the nature of the season so far that wickets have been pretty decent," said Parnell. "We bowled well in patches, but all in all a pretty decent day.
“It was nice to bat on if you got stuck in but there was always one ball that could get you out.
"We need to keep grinding away."
Parnell was playing his first game for the club after signing as their overseas import, and it was his first red ball match since September, 2019, thanks to the Covid-19 pandemic.
“I am still hungry to play and I wanted to come into a new environment and offer things on and off the field – those are the two massive things for me to return to England," said the South African..
“It felt weird bowling again. I bowled in a second eleven game a few weeks ago, but it was all about getting back into the match intensity again.
“Bowling in the nets is different to bowling in the game but a couple of good overs and I’m hoping to wake up tomorrow and feel young and fresh again.”
Glamorgan centurion Cooke felt Northants bowled pretty well, but that he and his team-mates took full advantage of the spells when they were able to get on top.
“It was a good contest between bat and ball," said Cooke.
"They bent their back and when they got the ball in the right areas there was enough there.
“But saying that there were times when the ball went soft and the pitch went flat and it became easy to score and get some momentum going.
"It maybe wasn’t an easy wicket to start on but once you got through that it got a bit easier."