please help me calculate the frequency

[na na]

Dear all,
  I am trying to find the frequency of extreme events ( higher than normal temperatures and precipitation) from 20 years of daily .nc data. I don't know how to calculate the frequency so I thouhgt that if I construct a loop through time it would work. So, I tried to construct a loop to pull from these 20 years only values of temperature higher than a certain value (for example tmax > 300K) but it didn't work and I don't know what else to do. Can anyone please please help me with an advice?
  Thank you,

  Diana Pop


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