Looking back at years since 1953, with a +QBO state and a monthly mean JAN SSN over 95 we notice that 6 out of 12 cases have a major SSW event in feb. Another 4 years have an SSW in JAN with only 2 in december. Whats important to note is that all the years with major december warmings had +PDO states and half the jan warming's had +PDO states as well. Also important is that no +QBO/smax years have even not seen a major SSW event, which is pretty striking.
Looking back at all years since '53 with a +QBO and low to moderate solar(JAN SSN below 95)
We learn that 14 out of 25 cases have no major SSW events all winter.... with just 3 out of 25 years having a SSW in DEC or Jan. These 3 years all had +PDO's. Another 6 out of 25 years in the data set had SSW in March or April, with no real PDO trends. There were also 2 years that had major Feb warmings.
So heres what we can pull out of this research:
1. In +QBO/Smax years SSW's are favoured in Jan/Feb and have always occured at least once per winter when the SSN is above 95 in january.
2. You are much more likely to see a SSW's in DEC when the PDO is positive or their is an el nino if the QBO is positive and SSN in high.
3.When the QBO is positive and winter SSN is low to moderate then you will most likely not see a SSW and if you do it becomes more likely to become a FW in march or april. Only seldom do you see a DEC/Jan/Feb warming and it helps to have a +PDO or el nino.
If solar flares continue to occur and the 30 day SSN continues to rise, we have a better chance at seeing a mid to late winter SSW and subsequent AO dip. This may be one of the only factors that can get us out of the overall +AO regime as many indices have been pointing to a stronger then normal vortex. If solar activity drops off again, its going to be very tough to see a SSW or sustained -AO period until March/april.