Sleet with a max temperature of -3 C ???
Notes:
The sounding shown above is a RUC analysis at AVP valid at 03z on December 16th. Note that the entire sounding is well below freezing, with a maximum temperature of -3 degrees C. The observed precipitation type at AVP at this time was sleet. One possible explanation for this observation is that the RUC analysis may have been wrong. Unfortunately, no ACARS soundings were available around this time to test that possibility. Another possibility is that the precipitation that was falling at this time was forming in a layer below the shallow dendritic crystal growth zone indicated by this sounding. Note that the crystal growth zone is very shallow, and located above 500 mb. Significant upward vertical motion is indicated in the layer from 850 mb to 500 mb, indicating that a large number of super-cooled water droplets likely developed in that layer around this time. The super-cooled droplets may have frozen due to cooling from evaporation as they fell through the surface-based dry layer shown on the sounding.
Slide 12