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Table of Contents

Note: HRES and 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.

Other causes of errors in temperature and dew point at 2m

Errors associated with thick fog.

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.

Errors associated with soil moisture.

Impact of Heat and Moisture Fluxes

Errors in the analysis of heat and moisture fluxes from the underlying ground have an important impact on the model surface temperature and moisture values and hence the derived 2m screen temperatures.  Fig9.2-9 & Fig9.2.1-10 illustrate the problem.   Low-level moisture can impact upon temperature forecasts; if humidity is too low then maximum temperatures can be forecast to be too high (e.g. East England and Germany).

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.

 

  

Fig9.2.1-9: An example of incorrect assessment of heat and moisture fluxes (left, temperatures; right, dew points), at Cordoba 12 June 2017.   Ensemble Control Forecast (ex-HRES) forecast temperatures and dew points (red) and observed temperatures and dew points (black).  Ensemble Control (ex-HRES) forecast has under-estimated the maximum temperatures by some 3ºC.  

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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.


 Fig9.2.1-10: Soil moisture 00Z 11 June 2017.  It is possible that there was too much moisture in the soil (yellow) when more arid conditions (brown) would have been more appropriate.  This is suggested by the observed lower dew points during the day on 12th June in Fig9.2-9.  Dew point errors are more likely to be indicative of soil moisture errors during the day, because there is much more convective overturning then. Conversely night-time dew point errors could be much more a function of very local effects - e.g. proximity of a lake or river.



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Fig9.2-11: An example of possible connection between IFS forecast 2m temperature (here using forecast EFI as a proxy) and forecast soil moisture content.  EFIs lower than -0.8 suggest extreme low temperatures compared to the model M-Climate and appear to be associated with high soil moisture content.  During the period, surface ground moisture appears to limit the amount of diurnal surface warming.  The reasons IFS are showing the temperature and moisture differences and uncertainties in analysis and forecasts are not clear.  Possible causes and correlations: 

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Users should assess the analysis of temperature and moisture in the area against observations, and modify forecasts accordingly.

Summary of Soil temperature errors:

Soil moisture and temperature is modelled in four soil levels but there is a considerable lack of real-time observations of soil condition and moisture content.  Nevertheless heat and moisture fluxes have an impact on model surface and 2m temperature and moisture. 

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Flooding may occur after heavy or prolonged rainfall but will not be modelled.  Incorrect soil characteristics and/or a water surface will cause errors in the forecast low-level temperatures.

Suggested considerations to offset soil temperature and moisture errors

The forecaster should assess the potential for error due to the above factors by:

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