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Don Paul: Have we turned the corner on harsh winter weather?

(NOAA)

Let’s begin with this experimental product from the National Weather Service’s Climate Prediction Center:

This probabilities map going out in time about a month suggests that much of the time, the areas in brown are going to be experiencing temperatures above average for this time of year. That won’t be every day, mind you, but in the next few weeks we are undergoing a pattern change that will bring us a lot more air of Pacific origin than arctic origin. I don’t always find myself in agreement with the Climate Prediction Center, but there appears to be good evidence supporting this change.

This change is quite different from what I was expecting for mid- and late February a few weeks ago. At that time, probabilities were fairly high that February would end up being a colder-than-average month. It certainly has been that up to this point.

Below is a similar CPC outlook for the month issued in January.

(NOAA)

Now, for a host of reasons, probabilities favor the cold dip in the polar jet stream that has been in the Great Lakes to shift back to the west central United States, with a warm, high-pressure ridge setting up shop in the east.

Just look at the shape of the upper level circulation on this map, noting the warm reds and the cooler blues. Arctic air is being directed toward the Rockies and plains, while a southwest upper level flow dominates over the Great Lakes:

(Weather Prediction Center/NOAA)

There is an oscillation between the sea and the atmosphere that centers from the Indian Ocean to the tropical Pacific, which has eight distinct phases as it shifts from west to east. It’s called the Madden Julian Oscillation (MJO). Its phase can usually be predicted out to two weeks in advance. Here is an illustration:

(Climate Prediction Center/NOAA)

Please DON’T try to decipher this graph. Allow me to oversimplify for you. Models are indicating the MJO will be stalling where all the squiggly lines are congregating in Phase 7.

What the heck does THAT mean? For purposes of this article and our extended range outlook, all you need to know is that a Phase 7 in February with an ongoing La Niña (as we have) has been shown to correlate with that western cold trough/eastern warm ridge in North America.

Okay, if you’re really a curious soul and want to learn more about this very complex sea-air oscillation, here’s an esoteric NOAA article on it.

In any case, this MJO variable in how the pattern is shifting is actually at least a part of why the shift is showing up in models for the next couple of weeks. The models are designed to incorporate the MJO into their calculations. Take the European ensemble mean (between 51 separate runs of the European model) for the upper-level flow. You’ll see where the warmer/orange shades are dominating, and the direction of the flow is shown in the black contours. (Just click on the middle arrow at the top to animate.)

The warm ridge dominates in the east over the time period that, of course, includes Western New York. There are occasional brief visits from colder blues in the trough to the Great Lakes, but they don’t stick around, as had been the case so often during this winter.

In addition, if you look at how the little, quick-hitting kinks (called short waves) in the flow are oriented, the true polar air doesn’t really make it to our location, and the bitter continental polar air masses stay north and west of the Great Lakes.

Yes, this pattern can suffer temporary breakdowns. There is also the possibility of a reversion to a western ridge/eastern trough by the time we get back to March, so I’m not suggesting we’re done with all harsh wintry weather. I’m just letting you winter-haters know nature appears to be cutting Western New York some slack for the next few weeks.

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