That was me, and it's a pretty commonly-used phrase in northern Whatcom County.
I think Phil mentioned that calling it a "thaw" is a bit odd, given that it's basically the opposite, which is fair. However, locally anyway, ZR events seem to be most likely to occur at the back end of over-running events, meaning their arrival tends to coincide with the transition from snowfall to snowmelt. Not sure if that's the real reason locals call it that.....but it works for me.