Winter wild card: Blocking
How those winter outlooks become exercises in humility.
Our story today noted that Accu-Weather is out with its winter outlook, and it's calling for above-normal snowfall, although not as much as last year.
It also sees the cold and snow arriving earlier than usual, and then the winter would take a milder turn.
At the risk of offending the intelligence of loyal readers, no one should be surprised if the winter plays out differently. This is still a primitive art form.
Interestingly, the idea of an early start to wintry weather is similar to that of both WSI Corp., in New England, which serves energy customers, and Commodity Weather Group, in Washington.
They all are counting on La Nina - the cooling of waters in the equatorial Pacific, over a continent-sized area. La Nina has developed, and the big question is how strong it becomes.
The beauty of changes in the ocean is that they can last for months and affect weather throughout North America for one or more entire seasons.
La Nina was a big player in the last year's seasonal outlooks. The consensus was it would be an unexceptional snow winter around here. Instead, Philadelphia measured 44 inches, the eighth-snowiest winter in the 125-year period of record.
Last winter, the La Nina shared the planet with an extraordinary period of atmospheric "blocking." That knocked the block off the oultooks.
It is a complicated phenomenon, but in simplistic terms the atmospheric flow gets stuck.
Winds tend to travel west to east, but on occasion the flow becomes persistently north-south over the North Pacific or North Atlantic, and that creates a traffic jam.
That can allow cold and storms to pick on a given area, as we saw around here in the last two winters.
The Commodity Group says that conditions, including increased Eurasion snow cover, again should favor blocking.
Accu-Weather's Paul Pastelok said that one factor contributing to blocking could be the melting of Arctic sea ice. In the far north, the overlying atmosphere is interacting with sea surfaces for the first time in who knows how long.
But Pastelok said that even if this is another big winter for blocking, it may be someone else's turn to send in the plows.