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M-climate is updated twice a week, every Monday and Thursday, and is based on 00UTC runs only (there are no 12UTC re-forecast sets).  The new files start to be used from the 00UTC run the next day.  So if one compares, for the same lead-time, the M-climate quantile plots (eg for a Thursday 00UTC run), and a run 24hrs later, they will be slightly different.  These limitations of twice weekly updates to the M-climate can be significant.  These can be particularly evident in spring and autumn when mean temperatures are changing most rapidly day by day.  The same M-climate set is used for 00UTC and 12UTC ENS runs in order to avoid inconsistencies between the validity period of the ENS and M-climate (e.g. we use the day1 and day2 M-climate distributions, with respectively, the T+0-24h and T+24-48h forecasts from 00UTC runs, and the T+12-36h and T+36-60h forecasts from 12UTC runs).

Note that up until the introduction of cycle 41R1 before Cy41r1 in spring 2015, the M-climate was constructed from a smaller number of re-forecasts, 500 in total, and as a result was more prone to sampling errors.

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