Mystery from last night solved. The two features circled in orange on this graphic are upper level (250 mb) closed lows:
Via the 06Z GFS run here’s the one just south of Charleston SC:
And here’s a very unusual upper low southeast of Florida out over the Atlantic:
I was too weary last night to figure this out. Kudos to Kevin Myatt who guessed this to be the case in his answer to my late evening question.
Now, here’s hoping there will be sufficient convective activity during this week’s cold front passage to warrant a chase. It’s a faint hope but I’m sticking to it.