Fiery sky

Why is fiery spelt like it is when it's based on the word fire. I always want to spell it firey, which makes more sense to me.

Anyway, this brief glimpse of the sun at 10pm this evening is about all I think we're going to see this weekend, whilst the rest of the country basks in 20-30ºC sunshine. It has its benefits living here, but also its drawbacks.