Nice post you might find this interesting
https://journals.ametsoc.org/jcli/article/28/9/3764/106758/Contraction-of-the-Northern-Hemisphere-Lower
Thanks Steve. It is good to see that what I thought was happening, is actually happening.
Interesting to see the mention of the poleward migrations of storm tracks, but I'm not sure it’s clear from this whether such change is the cause of the loss of "cold" air extent or a response to it, or, in fact, both. This from the abstract:
Cold years are characterized by an equatorward expansion of the jet in the Pacific and Atlantic sectors of the hemisphere and by invigorated cold-air production in high-latitude Eurasia and North America. Systematic poleward encroachment of the −5°C isotherm in the exit regions of the storm tracks accounts for nearly 50% of the observed contraction of the hemispheric wintertime cold pool since 1948. It is suggested that this trend is linked to displacement of the storm tracks associated with global warming.
Interesting also to note that December 2010 coincided with three periods of "extreme warm events" defined as more than 2 standard deviations, in the NH. Whilst not necessarily proof that you need an anomalously cold hemisphere for anomalously cold periods in the UK, its proof, I think, that warm periods (or indeed a warming world) do not prevent them!
Jeff
On the East/West Sussex Border
70m ASL