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All measurement uncertainty targets are stated as targets for standard deviation (estimate of random errors) as a measure of observation precision. Biases should be avoided; that is, related targets are close to zero. Observations should be made in such a way that any biases (estimates of systematic errors) of measurement systems form only a small part of the measurement uncertainty. This is one of the reasons why monitoring the observation bias (Trueness) separately is crucial for the WDQMS web tool. Targets within WDQMS follow the WDQMS Guidance Document (WMO, 2018), and consider mainly the use of “threshold” requirements (Table 6). However, considering the natural evolution of WDQMS and the tasks for the Regional WIGOS Centres (RWC), “breakthrough” requirements and “goals” are already introduced as descriptors (Table 7) in the quality maps (distinguished by different shades of green). The general definitions of these terms according to the WMO Rolling Review of Requirements (RRR) are:
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Whenever the WDQMS performance targets are revised, the targets defined in WMO RRR for the global NWP application area are taken into account. Table 7 contains the prescribed exceedance limits of measurement uncertainty for the variables monitored by WDQMS as defined by WMO RRR.
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