When is it time to start painting outside? You've got an exterior that is itching to get some paint on it, but there's still a chance of snow... Don't take the risk. Wait for the right weather and you'll rest assured that your new paint job will last as long as it should.
It's ok to paint outside when it stops freezing at night for at least a couple of weeks. Once the forecast looks like it's in the 60's and dropping down to the 40's at night, then it is fine to paint outside. The last thing anybody wants is premature paint failure by jumping the gun, so it's better to fault on the safe side and wait for the weather to warm. I'll most likely begin the first exterior the first week of May.
What about Indian Summer? So you've got 1-2 weeks of unseasonably warm weather in November or even March. Go ahead, but be careful. Make sure that you apply the paint during the warmest part of the day and that there is ample time for the paint to dry before the cold, moist air comes in at night.
Eric