Snow and ice pellets raise a number of concerns
- Runway Contamination
- Engine Ingestion and Induction Air Blockage
- Flying Surface Contamination
- Possibility of encountering freezing precipitation when higher
Density of the precip has a major bearing on the first three items.
Ambient temperature comes into play when considering flying surfaces. If it's well below freezing, the stuff should bounce off untreated surfaces.
But if there's liquid content, the stuff is nasty.
And of course, pellets at one stage have considerable liquid content before entering below freezing temps -- I wouldn't want to be flying in that zone
