For someone who would ever analyse my records and compare them against the official records taken by the Bureau of Meteorology (BoM) they would find a few differences.
As mentioned in an earlier post I have been taking temperature records since 2009. The recordings I make are based on those shown on the BoM's public webpages. The webpages also show wind speeds and directions, rainfall, humidity levels, apparent temperatures etc., although I do not use those personally. I like to take note of any unusual readings such as high wind gusts or high levels of rain, but I don't actually take any daily recordings for these.
When it comes to recording daily extremes, BoM uses monthly 'blocks', which makes perfect sense, and they create a table of the extremes for each month. Daily measurements at 9am and 3pm are also recorded in this table. The table for February 2013 at Sydney Airport can be seen here.
According to this page of definitions the minimums shown are based on the minimum temperature recorded in the 24 hours to 9am, while the maximums are based on the maximum temperature recorded in the 24 hours from 9am. While this is the standard for BoM, I haven't been able to find any particular reason why it is this way. Rainfall measurements are also taken from the 24hr period prior to 9am. (If anyone has an answer for why this is, please let me know! :))
My recordings follow a more simple idea of the minimums and maximums for a calendar day. That is the 24hrs from midnight to midnight.
An example of a difference can be seen from the first 2 days of February 2013. BoM's records state the minimum and maximum for February 1 were 21.1C and 21.8C, while February 2's recordings were 14.4C and 19.9C. This is compared to my own records of 17.9C to 24.2C and 14.4C to 19.9C. So while February 2 is the same, there is quite a big difference between the February 1 recordings.
I know that BoM have given definitions for the recordings as mentioned above and that's fair enough, but I just don't understand why it is done like this. Based on that definition it is possible for a temperature recorded at 9:01am on January 31 to be the minimum temperature for February 1. Conversely, a temperature recorded at 8.59am on February 1 could be the maximum temperature for January 31. Compare that to the maximum recorded wind gusts which are actually done on a 24hr midnight to midnight basis.
I'm actually really curious to what others think about this. Or well, maybe they don't think about it, but the point of highlighting this is to show why I use the measurements from the 24hrs from midnight to midnight. At least then the temperatures recorded were actually done so on the date in question.
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