[pmahoney]

See "(Entry 4 of 5)", the second noun definition of spell [1]. "an indeterminate period of time" or "a stretch of a specified type of weather" as in, "we've had a long dry spell; I hope it rains soon".

It does not sound particularly strange or unscientific to me.

[1] https://www.merriam-webster.com/dictionary/spell

[JoelMcCracken]

“A fainting spell” also comes to mind. It seems a bit archaic but I think it’s clear and unambiguous.

[dang]

A perfect reply. Thank you.