Ok... I went back and ran some analogs using years with an Easterly (negative) QBO and the results ( to me) were a little surprising. I broke this down by month from November through February, and I broke each month down to three categories with a QBO index range of -10 to -15, -15 to -20, and greater than -20.
Without factoring in any other teleconnection patterns or ENSO state, these are the results. Keep in mind that the QBO records only go back to 1950, so we only have 67 years of data to work with which is a very limited data set. The years used are on each image and you can see all of the QBO values back to 1950 here.
What is surprising is that in addition to the strength of the QBO, the QBO effects seem to vary depending on the month, much like the effects of other teleconnections or the MJO. For example with the MJO, the different Phases have different effects depending on the season.
But based "strictly" on these numbers, November should be relatively cold if the QBO is between -10 and -15. Based on the last update to the index in September of this year, it was sitting at -15.28 and on a downward trajectory. (http://www.daculaweather.com/4_qbo_index.php). We are still waiting on the October index numbers and those should be out soon, but if the trend continues for November, it appears that all values of a -QBO indicate that our temperatures may end up colder than normal.
December seems to do well with low negative QBO numbers and as the easterlies strengthen, the cold changes to warmth. Obviously a strong -QBO in December is NOT what we want.
January seems to like weak negatives and really brings the cold when that happens. But make it stronger and it becomes warmer... unless it's really strong and the cold returns.
February begins the trend the other way with a weak -QBO showing warmth, but as you move toward a stronger QBO it gets very cold.
I as discussed yesterday, many winter forecast place a lot of emphasis on the state of the ENSO ie, La Nina or El Nino, and I'm sure you've seen the maps the say Nina's are warm and dry in the southeast during the winter. I'm thinking that some of those forecast may end up being wrong.
The effects of every indices and patterns modulate and change the effects of all the others, so you can't really make a blanket statement as to warm and dry. Plus the strength of the Nina changes the final outcome for our weather. Strong Nina's generally do mean warm and dry for us, but we are not expected to have a strong Nina and right now we are sitting pretty close to a neutral reading. To give you an example, take a look at the next two images that show past Nina's
As you can see, not every Nina was warm and dry, and there are a few other variables that may come into play this year that may change the effects of a La Nina.
The QBO or Quasi-biennial Oscillation is a quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found.
Yea, lots of weather speak there but the important thing to take away from all of that is that we generally have better winters during a easterly QBO than a westerly. Eastward phases of the QBO often coincide with more sudden stratospheric warmings, a weaker Atlantic jet stream and cold winters in Northern Europe and eastern USA whereas westward phases of the QBO often coincide with mild winters in eastern USA and a strong Atlantic jet stream with mild, wet stormy winters in northern Europe. Also, an easterly QBO tends to generate more negative NAO's (North Atlantic Oscillation) which helps to contain the cold air over North America.
It appears that this year we will have a easterly QBO.
I showed this image yesterday and it depicts the placement of ridges (+) and lows (-) during la Nina's, and how that changes based on whether you have a west or east based QBO. Notice that with an easterly QBO, the Bermuda ridge is suppressed south while a trough is also extended south over the central part of the country.
Let's look at another angle. The sun is beginning to "go to sleep" as it heads toward a solar minimum and that also has an effect on our winters. Notice in the image below how the ridge is suppressed even further during those low solar periods.
WeatherBELL released a few charts for the southeast that show what their internal "Pioneer" model thinks will happen this winter.
These bottom images show the effects of four parameters on our winter weather based on the forecasted state of each one, the ENSO (Nina/Nino), the AMO, TNA, and AO. As you can see, none of those are warmer than normal.
The final factor I'll talk about today is the potential for a Stratospheric Warming event. SW's occur more frequently during easterly QBO's and are always welcomed if you're a winter weather lover. SW events cause a disruption of the polar vortex, and depending on the strength, can dislodge some bitterly cold air south.
I'll be anxiously watching all of this as we head toward winter because as you know, I love winter weather. Not that I'd want to live all winter with cold and ice, but give me 4 or 5 good winter storms and I'll be good. :-)