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Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output where shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

Assimilation of screen temperature and derivation of forecast temperatures

Assimilation of 2m temperatures 

Assimilation of observed 2m (screen) temperatures began with Cy49r1 introduced in autumn 2024.  Observed temperatures, nominally at 2m height above the ground, are adjusted from station height to model height using a lapse rate of 5.5ºC/km.  However, to avoid introducing anomalous temperature information:

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Occasionally lower tropospheric temperature data has been given low weight during the analysis process.  Usually this relates to problems with assimilating the boundary layer structure in situations with a strong inversion, coupled with the fact that the background is a long way from the truth.  The analysis procedures tend to give lower weight to observations that show major departures from the first guess.  In particularly lower weight is given where there is little support from adjacent observations.  Such data can even be rejected completely.

Derivation of forecast 2m temperatures

Forecast temperatures, including for Meteogramsmeteograms, are derived from interpolation between model forecasts of 10m and skin (surface) temperatures:

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