That riming appears to have come to fruition. The Utah Avalanche Center reports "overcast skies and light snow, rime, and graupel" in the mountains this morning and there are multiple pilot reports along the Wasatch Front of light or light-to-moderate icing.
|Maximum icing severity analysis with pilot reports of icing annotated.|
Source: NOAA/NWS Aviation Weather Center
Riming and aircraft icing occur in clouds that contain large amounts of supercooled liquid water. Ice crystals have a difficult time forming at temperatures near freezing but warmer than -10C. Since there is some snow forming in the mountains today, obviously we're able to form some ice crystals, but there's also a lot of supercooled liquid water. The morning sounding shows why. Note the strong inversion at about 640 mb and that cloud top temperatures are near or just below -10C.