Once the MJO gets to phase 8 , it kills the southeast ridge and then the the polar vortex presses in. The coldest part of December is likely from the 15th to the 25th.
That's what the models are showing. Models are getting colder for the first week thanks to the negative epo. Mjo is on the way through 7 into 8 through December. Bigger press.
Typically yes but we will not know how much press there will be for days .
There has been a trend on the models with the PV getting further south thanks to the negative epo.