While cold air has begun moving south from Canada and cooling temperatures, as is the seasonal tendency in the last month, conditions remain warm and dry in the western third of the U.S. That puts the spotlight on that region and the likelihood of winter precipitation easing that dryness next spring. Forecasters expect a succession of low-pressure systems, or troughs, driving higher-than-normal expected snowfall in the northern Rockies, while the southern Plains look to have a generally mild winter. Cold air masses moving into the northern Plains and Midwest remain a major variable in the long-range winter outlook. The cyclical movement of polar vortexes will also be a variable to watch in getting a feel for how winter will unfold in the U.S. this winter. See more on the long-range winter outlook.