The -AO has been around since the start of Dec.
The main driver in the flip to cold sustained cold was the NAO, and then the PNA not being well + helped keep the active storm pattern going at the same time.
Just south of Little Rock had 14-18” of snow yesterday/last night. Officially, Little Rock has had 20.3” the past 4 days. However, areas just south of town are closer to 30” in the same 4 day span. .