We've had a moderate Stratosphere warming for the last 7 days.. It even maxed out >2,000, which is pretty strong.
https://ibb.co/kXmPbht
At this time of the year, 10mb warming correlates to -NAO in +20 days about 2/3 times. That puts it at Feb 2-10. LR models don't have the NAO negative right now Feb 2-6, so we'll see. (The correlation isn't perfect it could range +5-10 days.)
Some will say that we already had the -NAO effect, but I disagree, on the last day of this 10mb (in this image below), the 500mb NAO is positive, and the historical analysis shows that 10mb usually leads in time, although 500mb and 10mb are kind of lined up right now.
https://ibb.co/BK0hdy6