I can't speak for the lettuce, turnip, or arugula, but I once received 6" of snow on radishes, and they didn't so much as flinch. They were about 2 weeks old at the time. They can seriously resist cold!
"Imagination is more important than knowledge." -- Albert Einstein
I was part of that same snow storm being in Mo. I am also in the same boat as you with sprouts of this and that. Luckily the ground temps are warm so we should be okay. I am going to check on my lettuce here in a min.