Tropical Storm Bopha is forecast to weaken as it recurves to the east of Japan which will promote a trough in eastern north america in a week to ten days from now.
This favours a trough in the east between the 6th and 10th of december which will begin to trigger the pattern change I have been posting about lately. More cold air will begin to usher southwards into the prairies and northern plains before moving eastwards by mid december. Expect the models to trend stronger with this feature as we get closer to the event and warm members turn cooler effecting the mean. 12z GEFS shows the trough:
Even stronger and more frequent trough's will follow suit allowing the pattern change to take place with more western ridging as well as a west based -NAO pattern: