Matthew Munsey
I'm not sure that it's doing ptype probabilities, I think it's just a better way of drawing rain/snow lines.
Mike gave an explanation on the owner's forum to a similar extent.
Mike Gibson said:...if you zoom into the 250-500 meters/pixel level you can see the precip typing probabilities in action. Note how the rain/snow line is "fuzzy" and that you can see some rain pixels go deep into the majority snow areas. The density of the dots of any type in an area is proportional to the probability of that type.
Mike