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It is important to assess the likelihood of different types of precipitation, particularly those of a hazardous nature.  The method of assessment of assessment of the type of surface precipitation by the IFS models depends critically upon the temperature structure of the model atmosphere, which includes the layers through which the model precipitation falls.   But modelling of this can be difficult, especially if the structure of the model atmosphere is imprecisely defined.  

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• the kind of surface in question and its probable temperature before assessing the result of any indicated freezing precipitation.  
• the various physical effects of precipitation types when deposited on surfaces and the way IFS handles them.

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A more informative ecChart display of instantaneous type of precipitation is based upon ensemble output and shows the most probable type of precipitation but gives no information on any, possibly hazardous, precipitation having a lower probability.   Such information can be obtained by reference to the instantaneous type of precipitation meteogram/histogram product.

Fig8.1.8.4: ecChart forecast chart showing HRES/Ensemble Control forecast of instantaneous type of precipitation forecast DT 00UTC 20 January 2018, T+60 VT 12UTC 22 January 2018 (Same ecChart as Fig8.1.8.2).  A type of precipitation is shown wherever the forecast rate of precipitation is greater than 0.1mm/hr.  The types of precipitation are represented by colours: Green-Rain, Red-Freezing Rain, Blue-Snow, Dark Blue-Wet Snow, Cyan-Sleet, Orange-Ice Pellets.  Areas where precipitation rates are less than 0.1 are coloured grey.  

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Fig8.1.8.8A (left): HRES forecasts freezing rain (total over 12hr).  DT 00UTC 23 February 2018, T+72 VT 00UTC 26 February 2018.  Colour scale: Light Blue 0.0-0.2mm, Mid Blue 0.2-0.5mm, Dark Blue 0.5-1.0mm, Dark Red 1.0-2.0mm, Red 2.0-5.0mm, Pink 5.0-10.0mm, Orange >10.0mm.  The pin marks the location of Quebec City with the forecast 12hr total of freezing rain given in the probe information frame.  Freezing rain total values are not the same as accumulation of glaze or glazed ice although some proportional accretion must be expected.

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

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• Read more information on the updates to ecCharts regarding type of precipitation products.
• Read more information on the verification of type of precipitation products.
• Read more on the probability of precipitation type products (from page 2).
  

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