Here’s the answer: These 5 periods are the only two week plus long cold periods at ATL since 1950 that were during a -PNA:
- 12/29/1967-1/13/1968: 0.2” + 2 Ts of SN
- 12/1/1968-1/16/1969: 3 Ts of SN
- 12/27/1978-1/9/1979: 2 Ts of SN
- 1/24/1979- 2/21/1979: major ZR & 4.4” of sleet from different storms
- 11/27/2010-12/25/2010: 1.3” Christmas snow (only measurable one on record?) plus 3 other trace to 0.1” wintry events.
So, what did these rare five periods have in common to be able to get that longlasting cold during a -PNA? A -AO and a -NAO were both present every time with them being quite strong during most of these 5 periods. A -EPO was present only during 3 of the 5 periods….so, not crucial. ENSO wasn’t crucial. The key is the strong -AO and -NAO. Furthermore, note the multiple wintry precip events during all 5 periods.
This is relevant in case we never get out of the -PNA to see if there’d still be much hope for sustained cold in the SE. Whereas a +PNA would certainly be most preferred, these five periods show that given both a strong enough -AO and -NAO it is still a reasonable possibility.