Well we have about 3 1/2 weeks until winter is typically done here in the south. If we don't get anything by Feb 15, it's over 90% of the time.
I'll just talk about major winter storms at Atlanta right here. Out of 39 major SN/IP at ATL, 27 occurred fully on or before 2/15. 12 occurred on 2/16+, which is nearly 30% of them.
I looked at major SN./IP at ATL during just weak La Nina or neutral ENSO. I found 17 of them. Out of those 17, 5 occurred 2/16+. Again nearly 30% of them.
Major ZR's are different : 27 of the 31 occurred before 2/16 leaving only 13% for them for 2/16+. All 4 post 2/15 were actually in March oddly enough. 3 of them were during neutral ENSO..
Major ZR's just during WLN or neutral: a whopping 22 of the 31. Of these 22, 3 occurred after 2/15 (14% of them)
In summary in terms of major ZR chances at ATL, I think Monsieur Carrollton is close. But in terms of major ATL SN/IP chances, he's too pessimistic as it is more like only 70% done, not 90%.