The stratosphere, Pacific Jet, and a changing hemispheric pattern

A hemispheric pattern change is underway, and the effects will be felt throughout the United States quite quickly over the next few weeks. A dramatic change in wind speed and temperature in the stratosphere — near the very top of the Earth’s atmosphere — over the past few days, has re-shuffled the pattern throughout the troposphere — where most of our weather is observed. This is especially true in the higher elevations, nearer to the poles, where the stratospheric vortex typically resides. The disruption to the stratospheric vortex will have implications on the pattern throughout the Northern Hemisphere.

Here’s the thing: The stratospheric vortex is fickle. It extends from the troposphere to the stratosphere, so simply disrupting it or moving it won’t have dramatic implications. But what’s happened over the past few days, and what will occur through next week, is more than that — forecast models continue to indicate that the stratospheric vortex will be completely split throughout multiple levels. When the stratospheric vortex splits into two, dramatic implications can occur throughout the higher latitudes. Even if they don’t occur immediately, the splitting stratospheric vortex can lead to a domino effect which changes the pattern down the road.

GEFS model showing a stratospheric vortex split at 50mb on the morning of October 28th, 2016.

GEFS model showing a stratospheric vortex split at 50mb on the morning of October 28th, 2016.

The particular split of the stratospheric vortex was peculiar in its origin — it actually was initiated from the troposphere upward. A few weeks ago we spoke about a very anomalous ridge in the Kara Sea. This ridge, with the aid of the remnants of Hurricane Nicole absorbing into the tropospheric Polar Vortex, had dramatic effects on the vortex as a whole. A weakened stratospheric vortex would eventually succumb to warming from multiple angles, and today, officially is “split” at 10mb, 30mb, and 50mb.

Forecast models, as a result, show the development of high latitude blocking, and a very active and anomalous pattern. But it isn’t quite as simple as “High latitude blocking leads to cold air in the United States”. In fact, it’s quite the opposite, at least initially. The extremely anomalous pattern is helping to amplify the Pacific Jet, which will become the most dominant jet stream feature on the globe within 5 days time. This will help to increase storminess along the West Coast, and flood the United States with warmer than normal, maritime air.

The warm air will be quite anomalous, especially in the Central United States, where temperatures could average 10 or more degrees above normal for a prolonged period of time. Forecast models suggest the development of a large area of ridging extending from the Southwest US Desert into the Ohio Valley for the first week or so of November. The Pacific Jet’s influence on the pattern will also likely cause a more active storm track, with above normal precipitation from the Plains to the East Coast.

5 Day Average temperatures will approach 10-15 degrees above normal across a large area of the Central US next week.

5 Day Average temperatures will approach 10-15 degrees above normal across a large area of the Central US next week.

The changes continue…

The hemispheric pattern won’t be done evolving at that point, however. The most significant, and noteworthy, change to the pattern will likely come during the middle of the month of November. Models suggest that the stratospheric vortex is going to remain under attack, with warming pushing into the poles from Siberia and Eurasia. High latitude blocking is forecast to persist, as the mid latitude wave pattern begins to retrograde.

The development of this process would be significant for the United States. A trough near the Aleutian Islands of Alaska would support more ridging on the United States west coast, supporting more troughing in the Central and Eastern United States. Both the long range GEFS and European Weeklies support the development of this process, while high latitude blocking becomes more established in Greenland and parts of the Pacific.

GEFS models showing a changing pattern across the entire hemisphere through Mid November.

GEFS models showing a changing pattern across the entire hemisphere through Mid November.

Over the next several days (and weeks) we’ll be closely monitoring the behavior of the stratosphere, as well as the Pacific Jet and higher latitudes, to get a better idea as to exactly how the pattern is going to shake down. How the hemisphere behaves through this time period will give us a much better idea as to how things will evolve through the early and middle part of November — and even into the month of December.

For now, we have an idea — and it features an active, colder than normal pattern developing by the tail end of November. Stay tuned!