The Canterbury horseman was originally coming south to tonight's meeting to drive a different horse, but has found himself in the sulky behind five horses over the 10-race card.
''It's a funny one, really - I was actually coming down for Sell A Bit and the field didn't get off the ground,'' he said.
''One thing led to another and I ended up with a nice book.''
The Dave Anderson-trained pair of Idolise (race 5) and Major Stride (race 8) look the best chances of McNally adding to his nine wins this season.
Idolise placed twice from seven starts in her first racing campaign last year, and warmed up for tonight's 2700m pace with a 1-length win at the Rangiora workouts on February 25.
''I spoke to Dave yesterday. He couldn't really be any happier. He thinks the horse is quite well and her manners are normally pretty good,'' McNally said.
The American Ideal mare led from the 1000m and sprinted the last 800m in 55.7 seconds which might be beyond some of her rivals tomorrow.
''If we got well away enough, we'd be at least handy, if not towards the lead. But the horse has probably got enough to be driven back in the field or put in the race.''
The richly-bred Major Stride - out of East Taieri mare Asabella - is in the ''same boat'' as Idolise, McNally said.
''He's come along quite nice in this preparation.
''He's got plenty of gate speed and I think he's got enough ability to be put in the race at Forbury. I'd say he'd be my best drive of the night.''
The Art Major gelding has had just three starts, including a win at Addington in late November before feeling the pinch behind Northern Derby contender Brilliant Strike on December 11.
''Everyone was pretty disappointed in him that night,'' he said.
''But Dave got his bloods done after the race and he was crook, so we'll let him away with that one. His prior form was pretty good.''
McNally gets the steer behind two trotters, with One Yankee Hall (race 1) and Glendaloch (race 9) needing to put their best hooves forward at the start.
McNally is more familiar with Glendaloch, having driven the Sundon 8yr-old in his last two starts.
''He's been quite good lately and he'd make short work of that handicap if he hopped off on the right foot,'' he said.
''He's probably a bit better than a place chance - we've got to hope he turns up on the day with the right manners.''
McNally's other drive is Twitch (race 3), and the removal of the blinds could spark up the 38-start maiden.
''With taking the blinds off, we're hoping that will change her mind space a wee bit and she'll put a bit more effort in that way.''
Tonight's meeting marks the re-opening of the member's lounge on the first floor of the southern grandstand.
Forbury Park Trotting Club president Gerald Cayford said there will be a barbecue and meat raffles throughout the night.
Members and prospective members are welcome.
Immediate past president Peter Gillespie will also interview leading drivers and trainers.
''What you see tomorrow night is what you'll get if you become a member,'' Cayford said.
