OK, so I get really obsessed with the weather this time of year, and spend a lot of time on weather boards and reading weather discussions.
The thing with seasonal outlooks is that they are very difficult and prone to error, that is why the long term NOAA predictions are all complete B.S. like 75% of the country is 'equal chance' of everything. You can predict that the winter will be 'cold', but is it going to be arctic cold for a few weeks in January and in the 40s in december, which averages to 'cold' or just plain cold the whole time?
I find the one to two month predictions by weather experts to be more accurate, although obviously very qualitative. Meteorologists make thes predictions based on interpretation of a number of atmospheric trends like the NAO, the QBO, seasurface temps, el nino and la nina conditions, and many other 'trends' that historically correlate to specific conditions. I'm not an expert on this but there are a number of oscillating atmospheric conditions that follow rough sinusoidal patterns, and meteorologists can look at a number of them, see the pattern, ie the NAO is trending negative and the QBO is trending positive and then compare that to past years with similar trends and from that predict future conditions on the scale of 1-2 months.Basically, it seems that November is going to continute to be warm, and near the end of the month it looks like we will shift back to cooler temps and we might have a decent december unlike past years.
Again, this is based on current analysis of the aforementioned 'trends' This could also mean that near the end of november it will get 'cooler' and then warm up again in December.
As for the longer range conditions, basically your entire winter weather pattern is controlled by the Jetstream. Generally, there will either be a trough in the east with a ridge in the west or vice versa. Eastern troughing gives cold temps in the east and warm temps out west. The position of the Jetstream also relates to what people call the "Pineapple Express" and can greatly influence snow totals as everyone in the PNW now knows.
The pattern of the Jetstream is what is influenced by the trends I discussed earlier, and is what allows people to predict the cooling trend in late november, this basically means a trough in the east. For the east to have long-term cold, this trough has to stick around, which doesn't always happen.
You have to remember that the Jetstream circles the globe, and is thus influenced by changes in Asia (upstream) and Europe (downstream). Upstream changes, such as the pattern of recent Typhoons in asia, can help predict 'downstream' changes here in the states. As well, downstream changes, mostly over the atlantic, can predict upstream changes here in the states. The most important upstream change is 'blocking' that occurs when a high pressure system sits over greenland, and 'blocks' the jetstream from changing out of an eastern trough.
On another note, One of the good things about this fall is that we have already had a decent outbreak of cold by late october, and significant snowfall in the east. We may get another storm next week, without the dumping of the last storm, but these early season cold 'outbreaks' are good in my opinion and sorely missed in past seasons with mild decembers.
Wow, that got to be a very long post. Remember I'm not an expert and this is just a huge summary of some of the things I've learned obsessing over the weather.
accuweather has great 'professional' content, including in depth articles and discussions about medium to long term outlooks by notables such as Joe Bastardi.