Can you cast area of effect spells so they effect an area 1 or 2 squares off the ground?

@JeremyECrawford Can you cast AOE spells (IE fog cloud) so they effect an area 1 or 2 squares off the ground (IE to confound flying NPCs)?

— Jeramy M. Pappas (@JMPappa) August 25, 2016

An area spell tells you if it must target an area on the ground or if it has some other targeting limitation. #DnD https://t.co/PLMzDnhDc0

— Jeremy Crawford (@JeremyECrawford) August 25, 2016