As others pointed out elsewhere, a strong wave packet on the subtropical jet which was generated by an ENSO enhanced CCKW in the Pacific, is important here too as it's circumnavigating through southern Eurasia atm.

You can actually see the momentum flux convergence from both theā€¦ pic.twitter.com/6XJgIrqq7S

— Eric Webb (@webberweather) December 15, 2023