Same goes for this stupid piece of shit http://www.wthr.co
And having such a prominent °F/°C switch is just baffling. This is not a function used regularly by the vast majority of users.
The spinner dial may not be functional, but it could be and should be, because weather conditions change incrementally and (more or less) predictably. If it's humid and cloudy and the barometric pressure is falling, then it would make sense for the spinner dial to move slowly between "cloudy" and "raining" positions, for instance.
And maybe the author of the app is an advocate of the metric system and wants to encourage users to treat the °F/°C switch as a prominent educational feature. Like I said, I don't know anything about it, but the amount of negativity being aimed at the app seems difficult to justify.