What's REALLY the sunniest city in the US? (statistics analysis)

When trying to find out the sunniest (and least sunny) US cities, every internet source seems to point back to this data:

but I’m not convinced that it’s very reliable. For example, it lists Little Rock Arkansas with a sunshine index of 62. But North Little Rock, 5 miles away and across a river, is listed with a sun index of 74!

Does anyone else see any other strange inconsistencies here?

How standardized are the collection and measurement techniques of weather stations in the United States (or even worldwide?)

How sure are we that these data are reliable?

Is it not possible that there’s some local feature that could explain the disparity? A river crossed by prevailing winds might have different weather patterns on either side, for instance.