The rain across the forecast area appeared to fall in four phases:
An initial shot of rain associated with isentropic lift, frontogenesis and reduced mid-level EPV.
A heavier band of rain, with embedded small-scale bands of extremely heavy rain, associated with isentropic lift, frontogenesis and reduced to negative mid-level EPV.
Convection associated with the cold pool aloft.
Light rain (and snow) associated with the cold conveyor belt.