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- predominantly dry snow (shades of purple) with fairly high probabilities.
- some indication of wet snow (shades of blue) with low probability and a few indications of heavy wet snow (black) with very low probability.
- some indication of rain (shades of green) with low probability.
- a few indications of ice pellets (brown/orange) with low probability.
- a few indications of freezing rain (red) with low probability.
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histograms of precipitation type in conjunction with charts of most probable precipitation type to assess the most likely precipitation type and the probability of alternatives. The histograms are readily available on ecCharts.
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Example of freezing drizzle
Freezing drizzle can be as much of a hazard as freezing rain. The "Probability of Freezing Rain" option on ecCharts can show 0% when the default threshold is used. Freezing drizzle can be seen if a very low threshold (say >0.01mm in previous 6hr) is applied.
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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.
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.
Fig:8.1.10-15: Forecast of freezing rain over Ukraine VT 06UTC 08 January 2024, DT 00UTC 06 January 2024. Colours show 6hr totals of freezing rain. Arrows show 10m winds. 2m isotherms in red. Vertical profile and type of precipitation histogram for Odesa, in the warm air.
Fig:8.1.10-16: Forecast of freezing rain over Ukraine VT 06UTC 08 January 2024, DT 00UTC 06 January 2024. Colours show 6hr totals of freezing rain. Arrows show 10m winds. 2m isotherms in red. Vertical profile and type of precipitation histogram for Kryve Ozero, in the area of freezing rain. The vertical profile shows temperatures above 0°C in a layer about 1000m thick.
Fig:8.1.10-17: Forecast of freezing rain over Ukraine VT 06UTC 08 January 2024, DT 00UTC 06 January 2024. Colours show 6hr totals of freezing rain. Arrows show 10m winds. 2m isotherms in red. Vertical profile and type of precipitation histogram for Kyiv, in the cold air.
Fig:8.1.10-18: Forecast of freezing rain over Ukraine VT 06UTC 08 January 2024, DT 00UTC 06 January 2024. Colours show 6hr totals of freezing rain. Coloured spots show type of precipitation. Vertical profile and type of precipitation for a location near Uman, on the northern flank of the area of freezing rain. The vertical profile shows temperatures just above 0°C in a thin layer. Orange spots show ice pellets.
Fig:8.1.10-19: Forecast of freezing rain over Ukraine VT 06UTC 08 January 2024, DT 00UTC 06 January 2024. Blue/purple colours show 6hr totals of freezing rain. Red/orange colours show precipitation extreme forecast index for precipitation. Arrows show 10m winds. 2m isotherms in red. Insets show EFI and CDF for 24hr precipitation for point with pin west of Odesa.
Fig:8.1.10-20: Surface analysis from Met Office VT12UTC 08 January 2024. The area of freezing rain is shown as an upper warm front.
Further information in the forecaster user guide
For more information on freezing precipitation see:
- Section 2.1.5.6 Types of Precipitation
- Section 9.7 Types of Precipitation - interpretation and effects
Additional sources of informationAdditional Sources of Information
(Note: In older material there may be references to issues that have subsequently been addressed)
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