The WIGOS Data Quality Monitoring System (WDQMS) web tool is the result of efforts by the ICG-WIGOS Task Team on WDQMS and of ECMWF (Prates and Richardson 2016), which further developed the web tool and hosts it with the support of MeteoSwiss and the WMO Secretariat (WMO, 2019). The current operational version of the WDQMS web tool provides four monitoring modules: the “Near-real-time NWP monitoring of the Global Observing System (GOS) networks”, the “Global Basic Observing Network (GBON)“, the “Monitoring of the Global Climate Observing System (GCOS) networks” and the "Transition Monitoring". The first module includes the NWP-based monitoring of GOS land-based surface and upper-air (radiosonde) observations as well as the marine surface observations. The monitoring categories, availability, timeliness and quality, are based on near-real-time monitoring information provided by four participating global numerical weather prediction (NWP) centres: the German Weather Service (DWD), the European Centre for Medium-Range Weather Forecasts (ECMWF), the Japan Meteorological Agency (JMA), and the US National Centers for Environmental Prediction (NCEP). The system aggregates NWP monitoring information by station, time interval, observed variable and NWP Centre and generates availability, timeliness and quality performance reports that are displayed as maps or time series. It should be noted that the marine surface component monitors only quality, which currently is based on information from three NWP Centres (ECMWF, DWD and JMA) only. The second module monitors all GBON- affiliated surface land stations and upper-air stations on land.  This module assesses GBON station-level compliance using data availability as the primary performance measure. The near-real-time monitoring information provided by the four NWP Centres is aggregated by station, variable, and time interval, and the calculated total number of reports are compared against the corresponding thresholds defined by the compliance criteria for the different station types.  The third monitoring module is based on data collected from GCOS monitoring centres and includes the monitoring of both GCOS Surface Network (GSN) and GCOS Upper-Air Network (GUAN). The GCOS monitoring is based on monthly statistics provided by DWD. The fourth module monitors the daily status of the transition from the Global Telecommunication System (GTS) to the newer WMO Information System 2.0 (WIS2), as well as the transition from Traditional Alphanumeric Codes (TAC) to the Binary Universal Form for the Representation of Meteorological Data (BUFR) format for both surface and upper-air land stations. The GTS-to-WIS2 status is determined by comparing the number of daily reports available on GTS with the number available on WIS2 for each observing station. The TAC-to-BUFR status is obtained by comparing the number of reports available in each format based on the observing station reports disseminated on GTS and WIS2. The transition monitoring relies on data provided by ECMWF that is independent of the NWP data assimilation system.

This User Guide is organized according to the entries and options available on the control panel of the WDQMS web tool to facilitate the users’ search of a particular option. Information on the monitoring module options as well as on monitoring categories are described  sections 2 and 3, respectively. Details of the temporal aggregation are given in section 4, and information about the participating NWP Centres in section 5. A summary of the products (maps and time series) available for the four monitoring modules covered by the tool is presented in section 6,  section 7, section 8 and section 9.  Section 10 provides a description of how to use the WDQMS API to access the information displayed on WDQMS maps. Section 11 concludes with  the References.