The October Snow Advance Index uses Northern Hemisphere snow cover anomalies to predict the Arctic Oscillation and United States temperatures in the following winter months. If snowfall anomalies are above normal, a negative Arctic Oscillation and cooler than normal United States is favored. In the same sense, below normal snow cover anomalies across the upper latitudes result in a positive Arctic Oscillation, which helps to prevent cold air outbreaks in the US.
The image at the top of this post shows projected snow cover changes over the next 192 hours from the September 19th 0z GFS (this post was made on September 19th). On the bottom right, the percentage change in snow cover over the 192 hour period is shown as +2.73%. This is the highest increase I have seen in the last 4 or so weeks of tracking the GFS and its snow cover change forecasts.