Posts

Miguel Pierre

Why the MJO and stratosphere are so critical for wintry weather in February

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As we move into February we are likely to see another change in the hemispheric weather pattern. Once again, changes with MJO/tropical forcing and in the stratosphere will play a major role in this shift. In our long-range outlook update on Saturday, we discussed these features and how they may potentially influence the atmospheric pattern. Here we will discuss what influence these climate phenomenon will have on pattern during the February and into first half March.

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Miguel Pierre

The role of the MJO and stratosphere in the long range pattern

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The pattern is changing — again. We discussed in an article on Monday how the Pacific Ocean will play a large role in the long-range pattern going forward. Currently, a jet extension in the Pacific Ocean is facilitating a progressive, mild pattern across the United States with storms tracking over the Central part of the country towards the Great Lakes. But tropical forcing and an MJO pulse will cause a deepening trough over Eastern Asia, with a developing standing wave (ridge) over the Eastern Pacific Ocean.

A huge change from the current state of the pattern, these developing waves in the Pacific Ocean are being caused by the MJO and tropical forcing developments, with additional impacts from the stratosphere. Lets dive in to the details of what is really causing the changing pattern — and why it’s so important.

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Miguel Pierre

What the stratosphere and tropical Pacific can tell us about December

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For the better part of the last three weeks, our forecasters have been discussing and monitoring the potential for a pattern change throughout the hemisphere. Medium range model guidance has often been gung-ho with the pattern changing within 7 days. As is often the case, forecast models were too quick to change the pattern. Much of this has to do with poor forecasting of the stratosphere and tropical Pacific ocean. Not coincidentally, these two features can give us clues as to where the pattern is heading in the weeks ahead.

As it stands this afternoon, model guidance and ensembles are in good agreement that a -NAO (North Atlantic Oscillation) pattern will develop over the next two weeks. This pattern is often defined by large ridges or higher than normal heights in the atmosphere over Greenland and the North Atlantic Ocean. -NAO patterns can allow cold air to be displaced farther south into the Northern 1/3 of the United States, particularly the Central and Eastern United States.

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John Homenuk

The stratosphere, Pacific Jet, and a changing hemispheric pattern

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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.

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