https://www.weather.gov/wrh/hazards?obs=true&wfo=gyx&hazard=true&hazard_type=all&hazard_opacity=80&tab=legend
Choose the obs tab and zoom and increase the density
Either maybe something convective went through and it was heavily rimed flakes/graupel or maybe nucleation is getting poor at times and you’re getting supercooled droplets in the cloud layer freezing in the cold dome.