Can kind of make out 2 quasi-distinct MJO waves in the Western Pacific in both the analysis + forecast fields through Dec 10 on the CFSv2. The first wave is north of the equator in the NW Pacific, having already developed a few days ago, whereas the second wave forms out of the South Pacific Convergence Zone (SPCZ) in a more classic manner for this time of the year, which is a big reason why you see models like the EPS showing the MJO completing a loop-de-loop in phase 6 through mid-month.
The GFS & CFS try to push the wave out into the Central pacific by the 3rd week of the month, but these models have a habit of progressing MJO waves far too quickly across the Maritime Continent & Western Pacific and I think they're a bit fast once again (& thus too fast w/ the pattern change away from the SE US ridge thereafter). Furthermore, the La Nina will help decelerate this MJO wave as the advection by the background flow (i.e. westerly jet stream) is weaker than usual, and enhanced convection underneath the ENSO standing wave over the Maritime continent will favor increasing amplitude of the MJO (again favoring even more warmth in the east-central US mid-month), which augments the downstream planetary wave pattern, also helping to slow the wave down (as those waves obtain higher amplitudes and tend to retrogress westward in the means). All of this points to an extended warm-up that could last through the 3rd week of the month (dec 14-21) and while we're talking pretty far out, confidence is higher than usual in the outlook during week 2 & may grow more w/ time for later week 2 outlooks once the models initialize a more amplified MJO wave. (which is supported by literature)