Have Reptile Veterinary Questions? Ask a Reptile Expert.
This sounds like you havea small King snake basking on your porch. These are not Harmful to pets or humans. The will eat small rodents and insects. Joan
The stripes can Vary in with and size. This is a baby picture that I posted. It is one of the few black and white banded snakes. Joan
This is a link of Venomous snakes in AZ: http://myweb.cableone.net/azmilk/venomous.htm
You can look over the pictures, but these are not banded snakes like you have described. Please look them over and see if any resemble the snake you had seen. Joan