It was only 1-2 inches deep on average where it landed directly, but flood waters washed it into these thick deposits in low laying areas. The temperature was also only in the 30s so it didn’t have time to melt. It just floated down the streets and collected.
I think the skew-t would show some incredible temperature inversions north of the front last night. Wind and pressure time series would also be cool to see where downdrafts generated gravity waves. The wind shifts were on the order of 30 mph one direction, then 30 mph the opposite direction. Easy to confuse with rotation couplets. There were some in the Chicago area too with the initial elevated supercell there.