Looking at the screenshots, Dark Sky does something bad that I think most other weather apps do badly as well.

Specifically: each day has a range (low and high) but it's not clear whether the low is for the morning or evening, and they could be vastly different. You could have 10-15 one day then 0-10 the next day, and think "Ok, I'll go out tonight and bring a jacket but no hat since the lowest it'll get today is 10 and whoops, actually it's freezing by the time dinner's over.

There are so many ways apps could do this better. Like showing a vertical line graph rather than discrete bars, with the lows inbetween days. Or if you want to keep the bars, make them angled, so the low is closer to the morning/night it's associated with. Or even show 3 temperatures, not just two! (one being the low for the previous or next day or whatever)