call.
Adult female (although this one may still be 1-2 instars from maturity) hesperus, mactans and variolus frequently have remanents of their juvenile pattern as seen above.

A widow out in the open in broad daylight? That's highly unlikely unless there's something very wrong with her.

Update: I found an image with a transverse white stripe on the front of the abdomen-

Looks like mine but, judging from the stripe, of slightly lower rank. The spider was sluggish, but definitely alive. The day was very overcast.

It's funny you should mention that. I have noticed that cobweb weavers and a few other spiders seem to be more active on cloudy days.

Thanks for the id and link. I'd checked the link earlier, but only in thumbnail form. I've seen two widows previously. Both were larger than this and very sleek and shiny. Looking at photos in the link upsize, I see a lot of variation and bet this is indeed a young widow. (The person who pointed me towards the spider will have a belated panic attack, if I let her know!)