At first, it's tempting to say that the atmosphere in the story is ominous: Phoenix Jackson is making her long, lonesome way through the countryside, and she's quite old; her eyes are failing her and every step must be carefully measured in order for her to stay safe. Indeed, it's...
a pretty precarious position: her shoes are unlaced, and it seems like the entire landscape is trying to catch her, and hold her:
Seem like there is chains about my feet, time I get this far . . . Something always take a hold of me on this hill—pleads I should stay[,]
she says to herself at one point. Once over the hill, she gets caught in a thorn bush, and the hot sun beats down on her. She has to clamber over a barbed-wire fence, and through the "maze" of "dead corn," after the "dead trees, like black men with one arm."
All of these images seem likely to create a suspenseful atmosphere, and indeed, there is a kernel of suspense in the story, particularly when the man who helps Phoenix out of the ditch points his gun at her. And yet Phoenix takes this sick joke in stride, just like she takes everything else in stride.
And so it's safe to say that the atmosphere, while partially suspenseful, is overall very assured and deliberate. It, like Phoenix, is calm and calculating; it is familiar. Despite coming up against so many obstacles on her way to town, Phoenix is always in control of the situation, keeps her cool, and rises to every challenge. And not once does the reader doubt her abilities—Welty gives us no reason to question Phoenix's competence.
But all this is true only because Phoenix knows herself and knows her path. She is very, very old and has been making the trip into town her entire life. Welty says that she
would have been lost if she had not distrusted her eyesight and depended on her feet to know where to take her . . . .
Every step of the way is ingrained in her muscle memory and her locative memory. If she had been placed in an area she was unfamiliar with, her feet would not have known the way, and she would have likely become lost, perhaps frightened, perhaps beyond saving in her frail condition. So if the setting had been any different, that suspense that keeps trying to snatch at the reader like the thorns that snatch at Phoenix would catch, and the atmosphere likely would turn ominous. But as Welty wrote it, this is not quite the case.