How long will Winter’s hiatus last? Look to the Pacific

Before the warmth has even arrived, signals of a changing weather pattern have begun once again. This is, honestly, par for the course in the hemispheric pattern that we have been locked into over the past several months. The progressive nature of the pattern itself has not allowed any particular regime to become stagnant. In other words, the pattern is changing quite consistently, and no overly cold or overly warm regime has become established locally.

While this idea fits within our overall winter forecast, there is something to be said for emerging signals of a return to a colder, more active pattern before a warmer pattern has already begun. Lets not get confused, though — the warmer than normal pattern is still on the way. In fact, temperatures are likely to average above seasonal normals in the Northeast US for quite some time from late this week through Christmas and into the first week of January.

It is then that we can begin looking for changes in the hemisphere. Medium and long range forecast models have already begun showing us these changes, with the Southeast US ridge, which will become a dominant feature from late December into early January, weakening and allowing room for colder air to sink southward from Canada. While medium and long range forecast models and ensembles can be inconsistent quite often, we can look around the hemisphere to see if their ideas have validity.

GEFS model showing a pattern in the longer range that would support colder air moving back into Canada and the Northern 1/3 of the USA.

GEFS model showing a pattern in the longer range that would support colder air moving back into Canada and the Northern 1/3 of the USA.

The search for a sensible forecast progression takes us to the Pacific Ocean. You may have noticed that this occurs quite often, and you’d be right — the weather patterns in the Pacific Ocean during winter have a huge impact on the sensible weather in the United States, particularly the Northern 1/3 of the Country. Recall the large ridge that built from the Pacific towards Alaska and the North Pole last month? That was the impetus for the extreme cold that surged southward into the Northern 1/3 of the US over the past two weeks, and gave us multiple wintry weather opportunities.

The opposite pattern to that exists currently, with a large trough building over Alaska and into the Northeast Pacific Ocean. This is helping to keep cold air locked up near the Arctic regions, with ridging building over the Southeast and Eastern United States. The overall pattern is expected to remain persistent for 7-10 days — but changes will already be underway across the Pacific Ocean by the time the near year arrives.

Multiple waves of ridging are forecast to surge eastwards through the Pacific Ocean — known affectionately as a “Wave Train”. These events are typically associated with changing hemispheric patterns, and not surprisingly the downstream effect on forecast models and ensembles is the idea that ridging will again return to Alaska, the Aleutians, and possibly even build northwards again towards the Arctic Region and Northeast Pacific Ocean.

GEFS model showing "Waves" of ridging progressing east through the Pacific Ocean.

GEFS model showing “Waves” of ridging progressing east through the Pacific Ocean.

That would be significant, as the development of another -WPO/-EPO would again force cold air out of the Arctic and down into Canada or the Northern 1/3 of the United States. The WPO and EPO are both oscillations where meteorologists monitor the atmospheric conditions in certain areas of the Pacific Ocean. The negative modalities of both of them suggest ridging in their domains, suggesting that cold air will be dislodged from those areas.

What’s to do from here? Continue to analyze the weather pattern. We can look at continuing signals for the development of this ridging, particularly in the tropical pacific where different areas of thunderstorms, lift, and forcing can give us clues as to when and where this ridging will develop. While we don’t know for sure exactly how it will play out just yet — our confidence continues to increase that a return to a pattern with “colder” risk will be here by the middle of January.

Stay tuned over the next several days and weeks for more information and supplementary posts and videos as more data arrives and our forecasting team continues to work on pinning down the forecast evolution!