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Fig:8.1.10-14 ecCharts presentation of ensemble forecast of probability of freezing rain accumulations, threshold 0.01 mm in previous 6 hr, DT 12UTC 24 January 2023, T+21 VT 09UTC 25 January 2023.  The vertical profile at Reading (located by the pin) shows a saturated layer of stratus at about 950 hPa with temperature above 0°C.  Very slight precipitation produced from the stratus by the model falls through an underlying sub-zero layer near the surface. The model gave above 65% probability of very light freezing precipitation.  Freezing drizzle was observed at Reading during the period.

Example of freezing rain

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Northward advection of warm moist air over Ukraine and above an undercut of very cold air from southern Russia and the North Caucasus region is depicted on charts as an upper warm front.  Vertical profiles at Kyiv and Odesa show the typical structure of the cold and warm airmasses.   Freezing rain at the surface occurs where the precipitating warm saturated air falls into the underlying cold relatively dry air.  The structure of the atmosphere at the intersection of the air masses is typified by the vertical profile at Kryve Ozero.  The precipitation area extended from Kyiv in the north to the Black Sea in the south.  Ice pellets were forecast on the northern flank of the freezing rain where the temperature in the warm air only just exceeded zero deg C.  Significant hazard may be expected where high extreme forecast precipitation indices intersect areas where freezing rain is forecast.   Users should be aware of the potential for freezing precipitation but note uncertainty regarding the extent, detail and changing limits of the layer with positive temperatures.  Much depends upon the detail of the structure of the airmass.

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