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• total snowfall probability,
• total snowfall rate probability,
• probability of combined events of wind gust and total snowfall.

Instantaneous, single member CONTROL-10

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/HRES

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A layer is availableon ecCharts to show type of precipitation.  This is for precipitation rates greater than 0.1mm/hr (shown by colouration).  However, these types of precipitation charts give no information on probability of the type of precipitation shown, or on any alternative types.  It is important to assess the temperature structure of the lower layers of the atmosphere to enable a tentative probability, or at least a risk, of potential severe weather types.

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Fig8.1.8.9A (left): CONTROL-10 forecast /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 do not the same as accumulation of glaze or glazed ice although some proportional accretion must be expected.

Fig8.1.8.9B (right): ENS forecast The ensemble forecasts freezing rain probability (>1mm over 12hr).  DT 00UTC 23 February 2018, T+72 VT 00UTC 26 February 2018.  Colour scale: Yellow 5-35%, Green 35-65%, Darker Green 65-95%, Blue >95%.  The pin marks the location of Quebec City with the forecast probability of >1mm 12hr total of freezing rain given in the probe information frame.

Histograms of Types of Precipitation

CONTROL-10/HRES gives no information on the probability of a type of precipitation and should not be used on its own;  reference should always be made to ENS output, particularly by use of the histogram, to assess the probability of other types of precipitation.  It should be remembered that an indication of freezing precipitation gives no information of likely accumulation of glazed ice although there must be a serious risk, and heavier precipitation rates suggest a potential  for greater accumulation.

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Fig8.1.8.10A (left): Type of precipitation forecast chart from CONTROL-10/HRES.  DT 00UTC 31 December 2017, T+84 VT 12UTC 03 January 2018.  The CONTROL-10/HRES forecast type of precipitation for a location in central Slovakia (shown by pin) is sleet (grey).

Fig8.1.8.10B (right): Histogram for the same location in central Slovakia (shown by pin in left hand frame) from ensemble DT 00UTC 31 December 2017, T+84 VT 12UTC 03 January 2018.  The most probable precipitation shown on the histogram is sleet (~20), but the histograms show a low probability of rain (~5%), but a significant probability of moderate or heavy snow (~15%).  Thus neither CONTROL-10/HRES type of precipitation charts nor ENS probability of type of precipitation charts should not be used without reference to the accompanying histogram.  Users should also note the height of the grid point used (always shown in the histogram heading) and assess the relevancy of the precipitation types to the precise location for the forecast which may be at a very different altitude.  Overnight between the 3rd and 4th of January there is a low probability (~5%) of freezing rain which nevertheless may be of significance to customers.

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Fig:8.1.8.14: ecCharts presentation of CONTROL-10/HRES forecast freezing rain accumulations over the previous 6hr, DT 00UTC 16 February 2023, T+42 VT 18UTC 17 February 2023.  The vertical profile at Bangor, Maine, USA shows the classic freezing rain structure of a very moist and precipitating frontal zone overlying the sub-zero layer near the surface.

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