Terry’s Take: The winter goes as October snow cover grows
NORTH AMERICAN SNOW COVER FORECAST TO SUBSTANTIALLY INCREASE OVER THE NEXT WEEK….
Did you know the (OSAI) October Snow Advance Index is an indicator that’s usefall to forecast how the Arctic Oscillation (AO) and winter temperatures will end up once the season begins. The SAI measures and applies Northern Hemisphere snow cover anomalies to predict the Arctic Oscillation and United States temperatures during the 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 United States.
This year the OSAI looks to start off strong as snow cover is expected to increase 2-4% by the end of September. This is the highest increase in snow cover since last years snow season came to an end.
This forecast increase is on top of the above normal northern hemisphere snow cover that already exists. The graph shows observed snow cover values (black) compared to normal (green) on the top image, with anomalies at each point on the bottom. Note snow cover is currently in above normal territory.
So what this all means is that there is a strong correlation between North American October snow cover and temperatures during winter. Snow cover keeps air masses colder and allows them to penetrate deeper into the country with less modification. (They keep their cold properties)! Simply put, the more snow cover that develops in October, the greater the chances for cold in the winter. Cold also increases the chances for more snow. That’s it in a nutshell.