Keep in mind that the air temp at plant level averages 5-8 degrees colder than the air temp at head height where the official readings are taken. Cold air sinks. :)

Assuming they have been well hardened off then why not wait until the temps actually are in the mid 50's and holding?

Dave

If they have been properly hardened off, they will be just fine.

My plants have been out since May 1st... Our temps went to about 49 last night, but it was only that cold for a very short duration of the night. Most nights have been mid-50s and most for the future appear to be the same. The highs have all been around the mid 70s and all my plants are doing very well.

It's all about the length of the cold exposure, in my experience. If the daytime highs are going to be 65-75 and it drops to around 48 for a couple hours on the nighttime low, it's not that big of a deal - not ideal, but not a deal breaker. The weather has been so wacky that if I were to wait until I were _sure_ of nighttime temps in the mid-50s, I wouldn't be able to plant out till June... And, at that rate, my late season tomatoes wouldn't get to produce much before they were killed by frost in October. It's one of the struggles of growing tomatoes in the NE.

That being said, at least for SE PA, after tomorrow night, there are no more nighttime lows below 55 showing up in the extended forecast... If you look ahead for your area, it might be better conditions on Sunday; You've waited this long, for one day it might be worth the wait.