Aleutian ridge, cross polar flow will lead to more wintry pattern
A pattern change discussed for several weeks is already underway, and will kick into high gear over the next several days. A much discussed ridge over Alaska will build northward later this week towards the North Pole. We call this a “poleward reaching” ridge — effectively named — as it develops towards the Arctic and polar regions from the North Pacific and Alaska. This is important for several reasons; but mainly because it helps to dislodge cold air which is typically bottled up in the arctic regions.
The ridge north of Alaska will continue to build this weekend into early next week — a very anomalous feature, even globally — and cold air will surge southward on its east end into the West and Central United States. This very same cold will eventually seep eastwards towards the Ohio Valley and East Coast. It won’t come all at once, in fact it likely will be in multiple rounds, but the cold will be anomalous.
GFS model showing multiple surges of colder air into the United States late this week through December 20th.
Very low heights will also become established over Canada as next week draws on, elongating from west to east and creating what is called a “Gradient pattern”. This develops as colder air becomes situated over the Northern 1/3 of the United States and, in response, warmer air develops throughout the Southern 1/3. While these gradients can take many forms, they often lead to enhanced precipitation and storminess near them.
Gradient patterns are a product of battling air masses at multiple levels of the atmosphere. While cold is surging southward from Canada and elongating from West to East over North America, the atmospheres natural balancing process allows warm air to develop along the Southern 1/3 of the United States, often of equal intensity. This time, it will be more relegated to the Southwest US on average — but still, it appears an impressive gradient will become established throughout the United States.
These gradients are important, to say the least: They can become highways for storm systems, which in this case could provide multiple opportunities for wintry weather. This will be especially true across the Northern 1/3 of the United States where it appears there will be plenty of cold air available to be tapped in to. Mixed precipitation events often become more likely near and along the gradient.
GFS model showing a height gradient at 500mb — allowing for colder air and an active storm track through the end of December.
In the Northeast US and Ohio Valley, the gradient will flex both northward and southwards, varying by day and depending on storm intensity. Individual storms are still hard to pin down, and forecast model guidance has not keyed in on any particular storm system just yet. One signal, however, is clear; there will be multiple (several) disturbances emerging from the Pacific into the United States and towards this colder, gradient pattern.
Our team will have more information on the developing pattern and storm threats as we continue to monitor data over the next few days. Stay tuned to our Long Range Dashboard and continue to keep an eye out for the latest forecasts and posts.
For now, feel free to check out the latest Premium Video as a supplement. The video details the upcoming pattern including the themes discussed above — and goes into detail on how and why the pattern will evolve bring colder, stormier weather to the Northern 1/3 of the USA.