Autumn began just a few days ago, but the weather pattern has already adjusted to the fall-like pattern with temperatures falling into the 30’s and 40’s at night. The first cold nights of the year typically come in mid to late September, as the warm and humid days of summer fade. The cooler, more crisp air gives us the first small taste of the cold winter which is only a handful of weeks away. The pattern has begun its seasonal change, and we are beginning to feel the effects of it. Yet, the best hints of what the winter pattern may have in store for us may be hundreds and thousands of miles to our north — over the high latitude/arctic region.
Seasonal forecasting can be a tedious and intricate task for meteorologists. Many times, meteorologists and forecasters alike find themselves drawing upon past events, analogs, and other research for help with predicting the months ahead. This is especially true in the Autumn season, as winter forecasting begins. Meteorologists are about to enter a flurry of forecasting over the next few months (yes, we are somehow enjoying this benign and calm weather right now). So as we look forward to the winter, we can often use the preceding months as indicators of the pattern to come. The pattern itself can often tip its hand, giving us a clue as to what we may be dealing with a few months down the road.
The words “high latitude blocking” likely will instantly bring back memories of some of our stronger storms and more volatile weather patterns in recent memory. The Blizzard of 2010, Hurricane Sandy, the Nor’Easter just a few weeks afterward. They all occurred during episodes of high latitude blocking, with a negative NAO cor North Atlantic Oscillation (for a background and more information on the NAO, click here). Still, high latitude blocking episodes which occur months before these events can often serve as accurate predictors, foreshadowing in a sense, of the upcoming pattern a few months after. A few months ago, we published some research on the blocking pattern during the month of May helping to predict the pattern during the summer months.
For a bit of reference, high latitude blocking refers to blocking ridges which occur in the higher latitudes over Canada and the North Atlantic (background on atmospheric blocking can be found here). These ridges slow down the jet stream/weather pattern. The high latitude blocking over Greenland, the North Atlantic, or Canada during the winter months often leads to the displacement of very cold arctic air over the United States, very often the Northeast US. The more amplified/slower pattern also leads to the potential for large coastal storm systems and has historically featured snowier and colder periods in the Northeast US.
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