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Met Office Numerical Weather Prediction models

Met Office global and regional NWP domains. The blue Euro4 domain is superimposed on the old green NAE domain. The purple domain is the UKV domain in 2016.

The Unified Model is run operationally, in a number of configurations, for weather forecasting at the Met Office.

Global and regional configurations

A global configuration provides the medium-range weather forecast and also supports the nested higher resolution regional models with boundary data.

More detailed short-range forecasts are provided by these high-resolution models which are able to represent certain atmospheric processes more accurately, as well as having a more detailed representation of surface features such as coastlines and orography.

The latest addition is a variable resolution UK model (UKV) which has a high resolution inner domain (1.5 km grid boxes) over the area of forecast interest, separated from a coarser grid (4 km) near the boundaries by a variable resolution transition zone.

This variable resolution approach allows the boundaries to be moved further away from the region of interest, reducing unwanted boundary effects on the forecasts.

Ensemble forecasts

UK ensemble forecasting, supported by a global ensemble, provide information on the uncertainty in short-range forecasts. The solution spread is obtained by perturbing both the initial conditions and also some aspects of the physical processes within the model. A medium-range global ensemble supports probabilistic weather forecasting out to seven days ahead.

Weather forecasting configurations at the Met Office

Model Grid length in mid-latitudes Grid points Vertical levels Forecast length Run times (UTC) Initial conditions
Global 17 km 1536 x 1152 70
(lid ~80 km)
6 days
(for 00z and 12z)
00, 06, 12, 18 Hybrid Incremental 4D-Var with MOGREPS Ensemble
UKV 1.5 km inner
4 km outer
950 x 1025 70
(lid ~40 km)
120 hours 03,15 Incremental 3D-Var
54 hours 00, 06, 09, 12, 18, 21
MOGREPS-G (global ensemble) 33 km 800 x 600 70
(lid ~80 km)

Control member + 11 perturbed members to 7 days
(remaining 33 perturbed members to 9 hours for hybrid data assimilation)

00, 06, 12, 18 Global analysis + 44 member ETKF perturbations, SKEB and Random Parameters Stochastic Physics, SST and soil-moisture perturbations
MOGREPS-UK (regional ensemble) 2.2 km 740 x 752 70
(lid ~40 km)
Control member + 11 perturbed members to 54 hours 03, 09, 15, 21 UKV analysis + 11 member perturbations interpolated from global ensemble. Lateral boundary conditions from corresponding global ensemble member.

Upgrades made to the UK models - November 2016

More information is contained in this Research News article from November 2016.

Crisis Area Models (CAMs)

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.

Differences compared to climate configurations

The weather forecasting configurations of the Unified Model differ from the Met Office seasonal and climate models in a number of respects.

  1. Data assimilation - in weather forecasting an accurate representation of the initial state of the atmosphere is vital and so assimilation of the latest observations is required.
  2. Resolution - the shorter forecast length allows the model to be run at higher resolution allowing more accurate representation of atmospheric dynamics and surface features.
  3. Coupling - processes which are not thought to have a significant impact on weather prediction timescales such as deep ocean circulation, atmospheric chemistry and the carbon cycle are not currently modelled. For example, while climate projections are typically run from coupled ocean-atmosphere models, the current NWP configurations use a fixed SST from the OSTIA analysis system.

Last updated: Nov 21, 2016 1:49 PM