Some known problems

IFS output is constantly monitored for bias or inconsistency between forecast and observed values and a list of inconsistencies is maintained and dynamically updated with a view to rectification of the problems.  Users also can play a part by identifying and reporting when certain weather parameters are being poorly forecast.  Focus should be on issues that occur repeatedly, rather than on one-off failures.  Notifications can be made by email to servicedesk@ecmwf.int (please use subject "Feedback on forecast performance").  Once it has been corroborated, an issue may be added to ECMWF's "official list" for attention and ultimate removal of the problem in a future release (Cycle) of the IFS models.  Keep up-to-date with known IFS forecasting issues.  It should be noted that those issues that have been marked as resolved (indicated by grey text in the link) will still be relevant when inspecting historical data.

Below are a few items.

Atmospheric model problems related to:

• Temperature
  • Inversions and low cloud can be poorly represented, notably in winter or high pressure areas. This has an impact on fog extent and persistence and also 2m temperatures. 
  • Supercooled liquid at  top of boundary layer cloud.  The limited vertical and horizontal resolution and uncertainties in the parameterization of physical processes near the cloud top leads to an overall reduction in supercooled liquid water with a detrimental impact on shortwave and longwave radiative fluxes, and increased 2m temperature errors over land.
  • See also the summary of 2m temperature errors and regional temperature biases.
• Precipitation
  • Investigations over USA have shown from April to September, an underestimation of precipitation occurs in the first half of the night while an overestimation takes place during the morning, both peaking in mid-summer.  Systematic biases are less pronounced during the rest of the day.
  • Sub-grid variability gives apparent biases of over-prediction of small totals, and under-prediction of large totals.  This is most seen with convective precipitation which has greater sub-grid variability than large scale precipitation.
• Snow
  • Snowfall in marginal situations and winter precipitation type.  The elevation, thickness and extent of the melting layer can be incorrectly modelled. This is particularly important where precipitation falls through it.
  • Surface fresh snow often takes too long to melt although ground temperatures are forecast above 0°C.
• Convection
  • Substantial convective outbreaks can be under-represented by HRES at higher latitudes and over flatter areas in Europe.
  • Sub-grid variability gives apparent biases of over-prediction of small totals, and under-prediction of large totals.  This is most apparent for convective precipitation which has greater sub-grid variability than large scale precipitation.
  • Inland penetration of showers triggered by sea-surface temperatures has improved but remains insufficient.
  • Convection can be over-represented in mountainous areas.
• Wind
  • There can be a bias towards under-prediction of wind strength at mountain sites.
  • Windstorms related to mountain waves can be completely missed by HRES (although captured by a Local Area Model (LAM)).
• Fog
  • Correct prediction of fog dispersal is notoriously difficult, because situations tend to be finely balanced.  The representation of near-surface inversions can be incorrect due to difficulties with energy coupling with ground and lakes.
• Monsoon
  • Indian and SE Asian Monsoons are too strong.

  Ocean Model Problems:

• • The Gulf Stream does not separate correctly in the western North Atlantic leading to incorrect warming/cooling of some sea areas.
  • In shallow waters, rapid changes due to upwelling can takeplace close to land leading to incorrect sea-surface temperatures.
  • Sea temperatures and salinity may not be correct in coastal waters (where there may be fresh water and lower salinity).
  • Locally incorrect sea ice cover (e.g. the gulf of Finland tends to be relatively uniformly covered with sea ice of a set concentration, or just open water).
  • Summer melt-ponds in sea ice sheets should be retained longer as sea ice.
  • Spurious sea ice can also occur also in deep water.
  • Spurious areas of ice act as if an island causing reduction of wave heights downstream.
  • Observations are not used in regions where the model sea depth is less than 500m in order to avoid assimilating data on the continental shelves where the ocean model has poor representativeness.
    
    

Additional Information

(Note: In older material there may be references to issues that have subsequently been addressed)

• Keep up-to-date with known IFS forecasting issues.
• Read observations regarding recent use and verification of ECMWF products by Member and Co-operating States in 2016.
• Read observations regarding recent use and verification of ECMWF products by Member and Co-operating States in 2017.