1	Winter Weather Workshop Forecasting Precipitation Type Presented by Dan Valle
2	Winter Weather Workshop Using Thickness Good 1st Guess BE CAREFULL!!!!! Can miss warm layers aloft Most common: 1000-500mb 5400m
3	Winter Weather Workshop Using Thickness Partial thickness is better 1000-850mb (1300m) 850-700mb (1540m) 1000-700mb (2840m) Look for areas where thicknesses overlap
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8	Winter Weather Workshop Soundings Superior to using thicknesses Can be found at: http://www-frd.fsl.noaa.gov/mab/soundings/java/
9	Winter Weather Workshop Top-Down Precipitation Type Forecast Method Are cloud tops cold enough to form ice crystals Is there an elevated warm layer present? What is the strength of this layer? Is there a surface based cold layer?
10	Winter Weather Workshop Ice nucleization This is the process in which snowflakes grow Growth Occurs When Supercooled Water Droplets Collect On Activated Ice Nuclei And Freeze Ice activation occurs between –10 and –15 ^oC in clouds (T-Td < 3^oC)
11	Winter Weather Workshop If the snowflake encounters a warm layer on its way down… Then we can simply look at the warmest temperature of that warm layer to determine how much the snowflake has melted.
12	Winter Weather Workshop Max warm layer temp <1^oC Very little melting has occurred Max warm layer temp 1-3^oC Snowflake has partially melted Max warm layer temp >3^oC Snowflake has completely melted
13	Winter Weather Workshop What happens if the precipitation falls into a dry layer? If no temperature advection is occurring, then the atmosphere will moisten and cool to the wet bulb.
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15	Winter Weather Workshop The precipitation now approaches the surface…what type will we have?
16	Winter Weather Workshop If the precipitation remained all snow aloft but encounters a warm layer near the surface, If the freezing level > 1200ft, likely RAIN If the freezing level = 900ft, SNOW (60%) 600ft, SNOW (70%) 300ft, SNOW (80%)
17	Winter Weather Workshop The precipitation only melts a little in the warm layer, If the surface temp < 32^oF, then SNOW If the surface temp > 32^oF, then RAIN
18	Winter Weather Workshop Precipitation Partially Melts (1-3^oC) Assuming the surface is <32^oF If the max temp in the warm layer closer to 1^oC, then a mix. If the max temp in the warm layer is closer to 3^oC, then sleet. If the surface is >32^oF, then Rain.
19	Winter Weather Workshop Precipitation completely melts in the warm layer If the surface is <32^oF, then freezing rain. Sleet is possible if the surface layer is cold and deep enough. If the surface is >32^oF, then Rain.
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21	EXAMPLES
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34	Winter Weather Workshop References and Thanks to: Gary Schmocker –NWS St.Louis Jim Kramper – NWS St.Louis Jonathan Howell – NWS Memphis