Here we go... the westerly winds of the upper-stratospheric polar vortex have begun decelerating. These will reverse to easterlies during Monday, culminating in an official "major sudden stratospheric warming" (daily-mean easterlies at 10 hPa & 60°N), probably on Wednesday 15th. pic.twitter.com/nVzW4Vu9Gj

— Dr Simon Lee (@SimonLeeWx) February 11, 2023