CUT-OFF TIME

NWP models that are used in operational meteorology must have a nominal time at which the 'gates are closed' to new data, and the forecast computation cycle is started. For models used for primary forecast guidance at short lead times, only a couple of hours at most is allowed after the nominal data time. So for example, the cut-off for 12UTC data might be around 1345UTC. For global models, i.e. those used for international aviation, a slightly longer time is allowed, but usually no more than 3.5hrs after data time. However, some centres (e.g. ECMWF) with less demand for immediate products allow over 9 hours or more of data to be assimilated.