At what temperature outside will the tanning really begin? Should I wait until it's at least 50 degrees (fahrenheit)? Maybe less, maybe more? I am trying to begin tanning outside at early as possible this year to have some color by the start of June and I am not trying to use a tanning bed at all.
It's not necessarily about temperature, however it generally is directly proportionate.
The figure you're interested in is UV Index. This gives a UV exposure figure based on temperature, cloud coverage, elevation, and a couple of other factors.
Just google ' UV Index'. There will also be a guide there on what each number means, it normally ranges from 0-12, I believe anything over 3 will alow you to tan, up to about 8 - anything over that and you'll still want to chuck on some factor 15-30 depending on your skin type and how you feel.
I pretty much use factor 15 even at lower levels.