The only requirement for snow to form is that temperatures are at or below freezing at all levels of the atmosphere.
(temperatures; below freezing; L:at all levels of the atmosphere) (The only requirement for snow; is; that temperatures are at or below freezing at all levels of the atmosphere) Context(The only requirement for snow is,List([0, 40))):(temperatures; are; at or below freezing at all levels of the atmosphere)
The only requirement for snow is,List([0, 40))
temperatures The only requirement for snow temperatures
below freezing is are
L:at all levels of the atmosphere
that temperatures are at or below freezing at all levels of the atmosphere
at or below freezing at all levels of the atmosphere