Another cold intrusion after the warm-up?

The Arctic regime covering the eastern two-thirds of North America is at once fairly strong, but will also prove to be short-lived. The prevalence of ridging in the West, as well as above the Arctic Circle may bring back another cA intrusion later next week, however, which I suspect is going to be an ongoing pattern for the first half of the winter season (DJF).

I notice a trend in the numerical models through November. Cold intrusions come southward from the Northwest Territory and Nunavut AR, while the western states build warmth. This cold vs. warm alignment scenario seems to alternate. The rise in temperature will mostly be focused across the southern half of the USA, while inbound Arctic regime finds a home in the Midwest/Great Lakes and Eastern Seaboard.

It is that constant reappearance of blocking signals (ridges) in the -WPO/-EPO/+PNA/-AO/-NAO sectors which creates the potential for more cold blasts. On the idea that snow cover will slowly build, the remainder of calendar autumn should not be particularly extreme in terms of the cold shots. But ultimately that situation will change. You need to remember that 90 percent of cAk events in the lower 48 states take shape in northern Canada. The rest of the cold intrusions come from Alaska, Siberia and Greenland. A falsehood spread in broadcast and social media in recent years is that winter air masses form in northern Russia and come over the North Pole into the U.S. In truth, “Siberian Express” or “cross-polar flow” episodes occur between once and four time a year.

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