loop -- please help

[I.A.L.]

Dear all,
I have some daily .nc data for 20 years (t  1 7300) for temperature and
precipitation. What I would like to do is to create some plots by
displaying for example only values of temperatures higher than 280 K for
the entire period of 20 years and make in in a bar plot. Can anyone give
me an idea, please? I am not familiar with looping and I don't know what
to do and I am desperate.
Thank you,