Looking at the latest run of the EURO weeklies it's apparent that the transition to fall is well underway. One of the most obvious signs is the snow that's forecast between now and October 29th. All of Canada and much of the northern and central Rockies are shown getting off to a snowy start.
A closer look at the central U.S.
If the snow comes to the magnitude shown across Canada it creates and intensifies cold air masses north of the border. You can see the cold developing below by the end of September.
All it takes is a jet stream buckle around a west coast ridge and down comes the cold. The JMA (Japanese Meteorological Agency) shows this for the mean 500mb jet stream flow December through February. Phasing between the northern and southern jets takes place far enough west to get the Midwest into the cold. That's a chilly look
While I'm not buying into it yet, the U.S. climate model the CFSv2 is on the El Nino band wagon. Look at the warmth it shows in its December-February temperature departures. Clearly it does not phase the 2 branches of the jet until the east coast. Nothing bitter about a split flow.
It's also drier than average implying below normal snowfall.
I'm still not settled on where this winter is headed but for my money the JMA with it's colder look (and better track record) seems more reasonable. That's the way I'm leaning right now with the cards just being dealt. Roll weather...TS