The operational NWP system

The operational suite does all the individual tasks that are required to produce a forecast.

• Observation processing — extracting all the observations that have been received, quality controlling them and finally reformatting them into a form ready for use by the model
• Reconfiguration (for some runs) — incorporating data fields from external files, such as the sea-surface temperature, or to update a climatological field
• Data assimilation scheme — adjusting the model background field, a forecast from a previous model run, towards the new data received from the observations
• Main forecast run — the length varies according to the particular run of the model

Using the forecast model data

The forecast data are written into files known as 'fieldsfiles'. Using these, various plotted charts and maps are produced, which forecasters then use to produce the weather forecast.

As it is important that the charts are available as early as possible the fieldsfiles only cover a 24-hour period. This enables charts for 24 hours ahead — T (current forecast time) +24(hours) to be plotted and made available even though the forecast is continuing.

Producing forecasts

Running a numerical weather prediction model is only part of the process in producing a weather forecast. Before a forecast is issued, the output from the model is studied by a forecaster.

For short ranges (hours ahead), the forecaster is able to compare a model field against actual observations. This means they can identify any possible errors, make appropriate allowances and possibly add extra detail to the model forecast — things like summer showers are often too small for the computer to pick up. The forecaster is also able to respond quickly and amend a forecast should the situation warrant it.

For medium-range forecasts (days and weeks ahead), the forecaster is able to compare the results from our model with those from other centres such as ECMWF (European Centre for Medium-Range Weather Forecasts), NC EP (National Centers for Environmental Prediction) and DWD (Deutscher Wetterdienst).

If all models are producing approximately the same solution confidence in the forecast would be high. Confidence is also decided by the consistency between model runs. If the model is consistent then confidence may be high but if it suddenly changes then confidence falls rapidly. In these situations the solutions of other models may be crucial. Sometimes, alternative forecasts may be issued with probabilities assigned.

This human-machine partnership is very important in producing accurate weather forecasts.

The Met Office disseminates various products from the operational numerical weather prediction models in GRIB and GRID formats.

The Met Office also has the capability to rapidly relocate regional models to any area of interest worldwide. These Crisis Area Models (CAMs) are run in support of allied military operations and disaster relief.