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ERA-Interim contains minimum and maximum temperature not per day, but for 3-hour periods.

If you need daily min/max temperature, you can calculate them as follows:

  1. Go to the ERA-Interim daily surface data web interface.
  2. Select the desired time period.
  3. Scroll down to the parameter selection and select the parameters 'Maximum temperature at 2 metres since previous post-processing' (Tmax, Parameter ID 202) and 'Minimum temperature at 2 metres since previous post-processing' (Tmin, Parameter ID 201).
  4. In Time and Step selection you now can only choose from time 00z or 12z and then step 3,6,9,12. The time is the forecast start time and the step is the number of hours into the forecast. For example, time 12z, step 9 gives Tmax and Tmin in the period since the previous processing at time 12z, step 6.
  5. Select all Time and Step values.
  6. Download the data.
  7. To calculate the daily Tmax find the maximum from all the Tmax values for one day, ie. from the values in time 00z, steps 3,6,9,12 and time 12z, steps 3,6,9,12.
  8. To calculate the daily Tmin find the minimum from all the Tmin values for one day, ie. from the values in time 00z, steps 3,6,9,12 and time 12z, steps 3,6,9,12.

If you need daily mean temperature, you can calculate this as follows:

  1. Go to the ERA-Interim daily surface data web interface.
  2. Select the desired time period.
  3. Select all Time values and Step 0. Time is the forecast start time and the step is the number of hours into the future. By selecting Step 0 (0 hours into the future) you tell the system to use analysis data, not forecast.
  4. In the parameter selection select the parameter '2 metre temperature' (2t, Parameter ID 167).
  5. Download the data.
  6. To calculate the daily Tmean integrate  (or, if you can not integrate, average) the four 2t values (00:00, 06:00, 12:00, 18:00:00) for each day.