I'm not dismissing anything, I'm trying to understand why it would produce an IP ptype with that sounding. You're right that it might be more complex than just being below freezing, but I can't imagine that there is a warm layer that the model uses in its ptype algorithm but it wouldn't show it in the sounding. This is what I found, it's generally over my head when it starts talking about max rain mixing ratio. https://journals.ametsoc.org/view/journals/wefo/31/2/waf-d-15-0136_1.xml