In WDQMS, timeliness refers to the delay in data transmission—via the GTS/WIS—between the nominal observation time of a message issued at an observing station and its reception at the NWP centre. The nominal observation time of a SYNOP message is typically HH+00. Hence, the timeliness of a SYNOP message is calculated by computing the difference between the reception time of the observations’ database time stamp of the NWP Centre and HH+00. Timeliness can occasionally be negative if the message is received by the NWP centre before the nominal observation time. Timeliness performance reports are generated by comparing 6-hourly, daily, and monthly average values (Table 3) against the thresholds defined in the OSCAR/Requirements. Note that negative timeliness values are excluded from the average calculations. Timeliness thresholds adopted for land surface observations are the ones outlined for high-resolution NWP applications: 15 minutes (goal), 30 minutes (breakthrough) and two hours (threshold).
Table 3 -Timeliness
Definition | Average of timeliness (T) values (as computed by each NWP Centre) over a defined period. |
Calculation | For each observed variable, the average of all valid data is computed for every station. |
Valid data | No negative data or data flagged as missing (-9999). |
Math expression | where Ti,j is the valid timeliness for time i, and variable j and Nj is number of valid data for variable j. |