"It didn't snow last week."
Just wondering, could a ge go after the shang? I think that's how I've usually seen last week/month/year written but I wasn't sure if it had to be different here
"上個星期" is valid Chinese for "last week", but "上個星期沒有下雪。 " and "上個星期沒下雪。 " are both rejected answers.
了 shows an action that was started in the past and completed. Since the action of snowing was never started nor completed, there is no 了.
It appears that any answer that uses a classifier ("個") for "last week" (i.e., "上個星期") is rejected as well as any answer that uses "沒", the short form of "沒有".
These were all rejected: