what night time temps will shut off tomato blossoming?

[mopinko]

finally starting to get tomatoes. what a shitty season. such a cold wet spring.
as usual, i want the fall to stay away. with the talk of el nino, i was hoping i would catch a break. but they are predicting at least 3 nights next week w lows in the 50's. i am in a little bit of a microclimate here, because of the lake, and also because my hugelpiles create a little warmth. might save me this time.

but, what is the trigger? when should i start to cry?