The importance of the Pacific Ocean in the U.S weather pattern

Thousands of miles away, in the Northern Pacific Ocean, a large ridge is develops in the atmosphere. This, if only by human nature, seems like a relatively inauspicious development at first. But its presence will be disruptive. Disturbances over the Western Arctic will be dislodged southward into Canada, cold air will push into the Northern 1/3 of the USA. The amplitude of the wave pattern will change. And suddenly, a snowstorm will develop along the East Coast of the United States.

Yes, we’re speaking in the past tense here. This already occurred, just a few weeks ago, during the most impactful winter weather event so far this winter in the Eastern United States. The root cause of the storm system, in relation to the atmospheric pattern, can be traced back to the Pacific Ocean, where a large developing ridge near Alaska completely changed what was an otherwise stale weather pattern.

Spoiler alert: It’s set to happen again. Medium range forecast models have come into good agreement on the overall evolution of the pattern in the Pacific Ocean which, as you may have surmised by now, will have an impact on the weather pattern throughout the lower-48. Changes are expected to our sensible weather which has otherwise been warm and without wintry weather for a few weeks now.

The truth is, understanding exactly how the Pacific Ocean is behaving is a critical part to any medium or long range weather forecast. The effects of what occurs there are almost always felt a few days down the road here in the United States. The weather pattern throughout the Pacific Ocean is often as interesting as it is complicated, and this winter has been no different.

Often times, the weather pattern throughout the Pacific can be best recognized by the periodic recurring wave events. Large-scale features, such as troughs or ridges, are best analyzed as “Waves” which are moving throughout the vast area of the Pacific Ocean. Understanding how these are behaving can tip off forecasters as to what is going to occur over the next several days and even weeks.

Over the last 5 to 7 days, the wave pattern of ridges and troughs in the Eastern Pacific has been in “Retrograde”. This means that the typical west to east movement of these features is reversing over time — so ridges are slowly backing from east to west. But over the Western Pacific, tropical forcing near the dateline has developed a “Wave Train” of ridges and troughs moving from west to east.

Like you often see at the shore, waves moving in towards the sand and waves moving away from the sand can collide. This is exactly what will occur in the atmosphere over the next 5-7 days as the retrograding ridge meets the incoming wave train. We call this “constructive interference”, and it will help to develop, at least temporarily, an extremely anomalous ridge in the North Pacific Ocean.

The development of this ridge will be significant in its own right. Higher heights over the Aleutian Islands and Alaska, building northward past British Columbia and into parts of the Western Arctic, will dislodge the overall circulation pattern there. Polar disturbances will be pushed southward into Canada with notable speed — and these disturbances may slide southward into the Northern 1/3 of the United States.

This is likely to lead to a few opportunities for wintry weather in the Northeast US or, at the very least, a period of colder air than we have been experiencing. The pattern is likely to remain active, with multiple disturbances impacting the area next week and into the first few weeks of February.

Exactly how the pattern in the Pacific Ocean behaves will have an impact on the sensible weather that we experience — and monitoring its behavior will be a major task for our forecasting team over the next few days. We expect that individual threats for wintry precipitation will likely come into focus over the next few days — so stay tuned!

But that’s not all! There is one more major player to consider in the pattern over the next few weeks. We’ll have a detailed post on the effects of the stratosphere on our weather soon.