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Meteorological day: Difference between revisions
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Most weather organisations in the world still to some extent remain consistent with the traditional way of working. This means that they report by '''meteorological day'''. Therefore, a key requirement for Steve Loft was to report daily derivatives based on a day that started at 9 a.m. Most weather software can only report daily measurments on a calendar day basis (since midnight).
Steve Loft did make a simplifying assumption that does not align with the practice of most Meteorological Offices, Cumulus
The following table tries to illustrate the divergence if you choose a rollover time other than midnight:
! scope="row"| Maximum temperature
| The daily maximum temperature in the 12 hours (9 a.m. to 9 p.m.) after the traditional observation time is assigned to the date that applies to both times
| Reported for day starting at
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! scope="row"| Average temperature
| The WMO says that daily temperature average is best calculated in
* Prior to automatic recording, some stations would have manual recordings taken a few times a day, and if these were at 0600, 12:00, and 18:00, the mean might be calculated by adding the 3 readings, then adding the last again (to compensate for no night-time observations), and dividing by 4!
* Nations are permitted by WMO to use integrated averages for their internal purposes. (By integrated all automatic measurements that are available, the reported average is a better representation for the entire day).
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! scope="row"| Rainfall
| Some nations report the daily rainfall for the 24 hours prior to the 9 a.m. observation time on a particular date. Others, throw their rainfall total back to previous date, i.e. the total for the 24 hours after 9 a.m on the particular date.
| Cumulus checks the current reading from a "count" supplied by weather station, it subtracts from this the count it stored at rollover time. From the count different, converted to required units, and calibrated, Cumulus assigns a rainfall total to the date when the day started.
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! scope="row"| Sunshine Hours
| Always reported by calendar day (midnight to 23:59)
| Regardless of which rollover time is selected, Cumulus always reports sunshine hours from one minute past midnight until midnight for any day. Note, MX does this efficiently, by using [[yesterday.ini]] if necessary; the legacy Cumulus 1 was dependent on internally held counts, so the calculation was wrong if that software was not running continuously.
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! scope="row"| Snowfall
| A snow day is reported by calendar day. The snow depth may be only reported at standard observation time of 9 a.m. (or as maximum that day)
| Processing changes by flavour:
* [[File:Badge vMx.png]] MX reports snow falling, snow lying, and snow depth, taken from the weather [[diary.db]]. If the hour part of the current clock time is less than [[Cumulus.ini#Data_Logging|SnowDepthHour]], the diary entry for previous calendar date is sought, for SnowDepthHour onwards it seeks diary entry with current calendar date
* [[File:Badge v1.png]] The legacy Cumulus reported just snow depth, but it used that to calculate the snow index for a month, year, or season. Again, it checks hour of clock time against [[Cumulus.ini_(Cumulus_1)#Read-only_parameters_in_the_Station_section|SnowDepthHour]] to decide which date to seek in [[Log.xml|Weather Diary]]. However, that diary could have any number of entries for any one date, so Cumulus permitted retrieval of any of those, but for snow index only uses last one of any date.
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! scope="row"| Highest and lowest pressure
| Reported for day starting at 9 a.m.
| Reported for day starting at
| Highest wind speed
| Reported for day starting at 9 a.m.
| Reported for day starting at
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