Frost in Late May? What the Heck?

[flummoxicated]

According to NOAA, there's a "slight chance" for frost Sunday morning and Monday morning; nighttime temps are supposed to be 37 and 39 F, respectively. I guess it's a good thing I'm behind on planting my vegetable garden, but I do have two hot pepper plants out, and I'm worried about the wisteria I planted. It did not take kindly to the April snow we had, even though I covered it with a heavy towel; it's only just now showing signs of recovery.

Wondering if anyone else is in the same situation. Wonder if my hydrangeas will be okay? Not so worried about the roses, but I just planted some smaller clematis. Guess there's nothing else to do but cover the plants in question, and sulk.

I'm in Zone 6a.