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Average temperature: Difference between revisions
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'''Annual summary line:''' | '''Annual summary line:''' | ||
The [https://library.wmo.int/doc_num.php?explnum_id=4166 WMO guidlines] say that for a climatic normal over an annual or seasonal period, the mean you quote should be the average of the monthly means you calculated for international exchanged products, but allow "National Meteorological and Hydrological Services [to] weight monthly normals by the number of days in the month when calculating the multi-month normal". In other words, within a nation you can report annual averages calculated using integrated daily means. If you are calculating climate norms for international publication you average the individual months. Put another way, within a nation you can add all the daily average temperature values you have and divide by the number of days (part or full year); for publishing climate norms you add all the monthly average temperatures you have for a past year and divide by 12. | |||
For Cumulus users looking at complete ''past years'' the difference between the two approaches just sometimes shows small discrepancies, and those are partly because of the way Cumulus does its rounding of each daily figure, rather than just rounding final figure. For the ''current year'', (or any past year if you have missing days in that year) especially in Northern Hemisphere Spring, the difference between approaches is seen because February and April have fewer days than January, March, and May, and when you look at a report the current month may have even fewer days. e.g. on 7 March one approach divides by 3, the other by 66 in a non-leap year (31+28+6 completed days, if none missing) leading to discrepancies, but in the same year on 1 April the first approach is still dividing by 3, but the second approach is dividing by 90. The latter shows little discrepancy because 30 (the 90 quoted divided by the 3 quoted) days is a reasonable average length for a month. So for good practical reasons, annual averages calculated from daily averages are good for Cumulus web pages as they are not skewed by missing days nor by incomplete months. | For Cumulus users looking at complete ''past years'' the difference between the two approaches just sometimes shows small discrepancies, and those are partly because of the way Cumulus does its rounding of each daily figure, rather than just rounding final figure. For the ''current year'', (or any past year if you have missing days in that year) especially in Northern Hemisphere Spring, the difference between approaches is seen because February and April have fewer days than January, March, and May, and when you look at a report the current month may have even fewer days. e.g. on 7 March one approach divides by 3, the other by 66 in a non-leap year (31+28+6 completed days, if none missing) leading to discrepancies, but in the same year on 1 April the first approach is still dividing by 3, but the second approach is dividing by 90. The latter shows little discrepancy because 30 (the 90 quoted divided by the 3 quoted) days is a reasonable average length for a month. So for good practical reasons, annual averages calculated from daily averages are good for Cumulus web pages as they are not skewed by missing days nor by incomplete months. | ||