A Negative NAO IS Friendly To Skiers. Right Now, It’s Smiling.
During the upcoming winter I will be producing condensed regional forecasts on a weekly basis, hopefully providing readers with another nugget of info before they pick a destination for time on the slopes. I will refer to a number of different reasons for forecasts that you will probably not hear from other sources. Things like the Typhoon Rule that I wrote about last week and SSW (Sudden Stratospheric Warming) episodes. In addition, I will use a number of “teleconnections” around the northern hemisphere.
A teleconnection is a relationship between surface and/or jet stream level features located thousands of miles apart both west to east and north to south. Each one has a correlation to different types of winter weather in different parts of the country. Examples are the SOI (Southern Oscillation Index), AO (Arctic Oscillation), EPO (Eastern Pacific Oscillation), and MJO (Madden Julian Oscillation). One of the most significant winter teleconnections for snow lovers east of the Rockies is the NAO (North Atlantic Oscillation), which I would like to explain today.
The components of the NAO are found over the waters of the North Atlantic and the teleconnection is based on the difference in sea level pressure between two persistent features: the Icelandic low and an Azores high. The relative positions and comparative strengths of these features determine the sign (positive or negative) of the NAO.
When the two systems are relatively strong, the interactive circulation between them (counterclockwise around the low to the north and clockwise around the high to the south) speeds up, which results in more of a zonal, or west to east flow across the Atlantic. That setup makes it easier for cold outbreaks from Canada to be ushered offshore after only a brief visit to the central and eastern U.S. This is an example of a positive NAO.
When the two systems are weaker, the flow can buckle more easily, not only at the surface but also aloft. When that happens, upper troughs are favored over central and eastern North America and blocking ridges can be found in the vicinity of Iceland and Greenland. This is the configuration when the NAO is negative.
Jet stream patterns are more persistent when there is greater amplitude of troughs and ridges. When the NAO goes negative, the trough acts as a receptacle for cold air from Canada. The development of such troughs often spawns surface storms, many of which bring snow to the Lakes, mid-Atlantic, and Northeast, often in the form of a disturbance that becomes a coastal “Nor’easter”. It is worth noting that a correlation exists between low solar activity (we are now very near the minimum of the 11 year solar cycle) and North Atlantic blocking patterns that support a persistent negative NAO. So, there is reason to believe that the NAO will be in a mode friendly to skiers and riders at least a fair amount of the time this winter.
Here are depictions of the two modes of the NAO…
Now that November is here I know that many or you are starting to get as revved up about the season as I am and you are looking for snow, or at least temperatures cold enough for productive snowmaking. The Rockies have gotten off a fast start and the first shot of true cold air has reached the Great Lakes this week and will spread into the Northeast over the upcoming weekend. The first half of the new month, at least, looks good for cold and some natural snow roughly north of I-80 from the Midwest into the Northeast. It won’t be long now.
Healthy senior man seeks healthy downhill skier & golfer in CO, CA, or AZ .