A negative (easterly) QBO helps create a blocking high over Greenland which can divert cold air south into the United States.
Thoughts about this upcoming winter. Through the fall, there simply was no overwhelming signal to point a direction for the winter. Currently, nothing overwhelming in my eyes, but hints and LOTS of differences from last year.
Differences are:
1- a more east based La Nina. Southeast ridge is further south.
2- a east Qbo, enhances a negative AO.
3- cooler waters off the southeast coast vs last year. The stubborn southeast ridge that continued feeding back off the very warm waters last year, will not be a reoccurring theme.
4- 30-40N on the dateline a hint of the cold pool that was there, faded and now returning and some warmer waters forming off the PNW coast. (that may been more than 1 thing) Enhances a +pna(western ridge)
5- A significant coverage increase in North America snowpack. Especially over Canada. While this can vary at any point, the locations currently covered, looked locked in. This can enhance cold air available when it comes.
6- MJO- short term, as this is not a long term prediction. Its been in the poor phases despite other signals being well aligned for cold to date. A zonal fast flow, has not allowed anything to dig and form and really entrench the cold. Things are zipping along, including moisture.
Snow cover extent- Snow cover is on the high side vs the past 13 years across North America and especially Canada. While encroachment into the U.S had been slowed by a zonal flow, its available when things get more favorably aligned. Which may be sooner than later. 
Current SST setup and 7 day sst change. While this is a constant flux, the trend has been going this way for weeks. Last winter I spent many many hours looking at SST reanalysis. Mainly during the very warm February. It matched 1932(an incredibly warm Feb and one that beat last Feb) well, and the 1932 transition from Feb to March transitioned almost in the same locations as this past year. That test was a success as models went to those analogs. This year, while I have not had time to draw up comparisons like I would like. The overall setup is a look of a more favorable east cold.
What I mean by that. 30-40N just east at the dateline a cool pool has been developing, with a increase in SST temps east of this. This should create more of a -wpo, and -epo. Ridging is more persistent along the west. The Southeast ridge, while is typical in La Ninas and a triple whammy last year with very warm waters off the southeast coast, a west based La Nina, and a westerly Qbo. All 3 are shown to favor a southeast ridge off the southeast coast. This in turn promotes a more consistent southwest warm flow and deflects cold pushes off to the north. Any intruding cold gets followed by a warm push.
Subtle differences in La Ninas with a easterly/neg qbo vs westerly. The Southeast ridge is much further south. Joe D’Aleo mentions this work often and plenty of examples.
The easterly qbo also enhances a negative Artic Oscillation which allows polar air to migrate from the polar regions and spread south. Low solar, which we are in now(not pictured) as well enhances a negative AO. During winter, Sudden Stratospheric Warming (SSW)events are more typical with low solar . When the stratosphere warm and propagates downward, enhances a cold push to lower levels and depending upon where this occurs, can cause major cold intrusions into the U.S. So, with the large N.A snowcover, should this pan out, we may have some extreme outbreaks in the heart of winter.
Our current MJO is in a unfavorable phase the next 2 weeks off the models. With hints of going into more favorable winter phases. This I believe occurs in the 10th-14th timeframe.
The current state of the teleconnections have not been bad. One thing to watch for, with the SST anomalies warming off the west coast is for the PNA to pop positive 2nd week of December. That will equal ridging west. By then with Mjo becoming more favorable, teleconnections in favorable cold positions, a trough east. This along with the other before mentioned keys, will equate to a cold 2nd half of December and going into the new year.
For anyone thinking its like last year. Nothing like it in the overall results. Also nothing like it in the hidden aspects we can’t see. This should equate to a winter, not like the last 2.
The Euro weeklies have shown consistent cold coming in December. The CFS is off the charts and changes dramatically at times. Hesitant to use it except when in line with other factors. The Euro weeklies are lining up with what the SST anomalies currently are looking like they are going to.
Conclusion on my thoughts-
A different winter than the past 2. A more consistent cold pattern with a east based qbo, east based la nina, a Pacific sst pattern resembling a winter with some good eastern cold. SST temps off southeast resembling that more as well. While at times things will bounce,with incoming troughs exiting on sw winds and warm ups. I expect those warmups to be just typical of what this area sees in the winter. Followed by colder periods. Storms can and will at times cut west. Leaving us on the wintry mix, to rain, back to snow. As that occurs, thats when the coldest air masses may intrude in behind those systems with lake affect and upslope events.
Overall- A slightly below normal temp winter. With potential of several extreme cold outbreaks.
Snowfall wise- Average to slightly above.
Allegheny Mountains Weather 