The temporal aggregation is presented in two different formats: 6-hourly intervals and daily intervals. In addition, an aggregation based on a 5-day moving average (Alert) is also available.
4.1. 6-hourly
The 6-hourly intervals are centred on the main synoptic hours (00, 06, 12 and 18 UTC) as described in Table 8.
Table 8 - Definition of the 6-hourly aggregation intervals. The defined time limits (note that 21UTC in the 00 interval refers to the previous day) are applied to the observation time (t) as specified in the NWP monitoring reports. It should be noted that only the observations that were made available in time for each of the NWP assimilation systems are included in the NWP reports.
6-hourly interval | Observation time (t) |
00 | 21 UTC ≤ t < 03 UTC |
06 | 03 UTC ≤ t < 09 UTC |
12 | 09 UTC ≤ t < 15 UTC |
18 | 15 UTC ≤ t < 21 UTC |
4.2. Daily
The daily aggregation refers to the union of the four 6-hourly intervals as defined in Table 8, therefore is the 24-hour period within the interval 21 UTC ≤ t < 21 UTC, where t is the observation time and the lower “21UTC” limit is the day before.
4.3. Alert
The alert maps represent a 5-day moving average, therefore rely on daily values for a 5 day period as described in Table 9.
Table 9 - 5-day moving average
Definition | 5-day moving average of daily averages |
Calculation | For each observed variable, the average of the valid daily values for that day and the four of previous days. |
Valid data | Data not flagged as NULL |
Minimum required valid data | It is calculated if at least 1 valid daily value is available over the 5-day period. |