Ice Pellets/Sleet Saturday Morning

 

Ice Pellets Saturday Morning 11/3/12 

Ice pellets/sleet have been reported with some of the showers south of Chicago this morning. This graphic, depicting the morning weather balloon sounding from Lincoln, IL, shows why there are some ice pellets with these showers this morning. Notice that there are three distinct temperature "layers" on this sounding. Above about 680 mb, or 10,000 feet AGL, the temperature is below freezing. Ice crystals, snow flakes and even some supercooled liquid droplets exist there. Below that, in the layer separated by the yellow dashed lines, the temperature warms to +2 to +3 C. Any ice or snow falling through this layer likely partially melts. Below that layer, the temperature is above freezing, but the dew point temperature is less than 32 F. Evaporative cooling in this layer may help re-freeze partially melted precipitation particles which then make it to the ground as ice pellets or sleet, despite the lower 5500-6000 feet of the atmosphere having temperatures above freezing in the sounding.  The red line sloping from upper right to lower left is the freezing line.



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