I'm posting some accompanying graphics on Dennis' behalf. First, the updated time series below shows the three main modes of variability in the Pacific: (top graph) ENSO (principal component-1), (middle) the North Pacific Mode (principal component-2), and (bottom) "The Blob" (principal component-3.

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Second image shows the three main modes of variability as maps. The opposite colors mean that there is an opposite relationship of temperatures in those areas: the warm and cool locations that appear in one phase will switch places in the other phase of the pattern.

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THe third figure is the SST patterns you get if you add together maps of each of the principal components according to their observed strength and phase in early winter 2020.

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Lastly, Hartmann asked me to post some graphics showing the patterns in cloudiness over the Pacific (the amount of cloudiness can be inferred from satellite observations of outgoing longwave radiation, or OLR) because thicker clouds block the escape of OLR from Earth's surface. Satellites will see less OLR than average when thick clouds are present, and they will see more OLR when areas that are usually cloudy are clear. He said via email:

The media regularly associates cold events like the recent one with the warming of the Arctic, but one can make a strong argument that this anomaly really came from the tropics.  The shift in tropical SST Associated with the first three modes of variability makes the tropical Pacific and Indian Ocean SST anomalously cold everywhere except in the West Pacific.  This results in enhanced convection in the West Pacific, which can be seen in the OLR anomalies.  This shift in tropical Pacific convection encourages the wave pattern over North America that ‘causes’ the extreme cold event.   This is all consistent with the arguments made in my 2015 paper.