Page History

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IFS model orography smooths out valleys and mountain peaks, especially at lower resolutions.  A forecast 2m temperature may be unrepresentative if it has been calculated for an altitude significantly different from the true one.   A more representative height might be found at one of the nearby grid points.  Any remaining discrepancy can be overcome using Model Output Statistics (MOS) or statistical post-processing (see additional sources of information below).

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The effect of lakes is parameterised using FLake and a lake cover mask.  The sub-grid detail may not be completely captured and the energy fluxes may well be incorrectly estimated, particularly where frozen lakes are plentiful and/or forecast snow cover is uncertain.   These aspects can:

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Errors in the representation of evaporation impact forecasts of near-surface humidity.  Leaf area index is a measure of vegetation coverage and determines the degree of evapotranspiration.  Higher values mean more evapotranspiration, and thus greater fluxes of moisture into the atmosphere.

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Some errors have occurred in forecasts near-surface data associated with cases of thick fog.  A bug in IFS has misrepresented the positive feedback between two interacting and imperfectly represented mixing processes in the near surface layers in the new moist physics scheme.  The problem has been added to Known IFS forecasting issuesand a fix has been prepared with implementation in the next IFS upgrade expected late in 2022.

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Land surface characteristics (soil moisture, leaf area index) have an impact upon temperature forecasts.    Significant differences in temperature can occur over a short distance where there is a sharp change of surface characteristics.   This can influence the location and development of subsequent convection.

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The right panel shows that on this occasion the magnitude of the dewpoint errors was even larger overall.   Again there are many possible reasons, but one candidate would be mishandling of moisture fluxes to/from the surface.  In turn these could relate to soil moisture errors, or errors in handling the biology of evapotranspiration.  

An influx of moist low-level air might also occur locally (e.g. effects of a strong sea breeze).  This can influence the location and development of subsequent convection.

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