This is an update to the article I posted in October about our upcoming winter. At that time, I discussed the developing El Nino and its typical impact on our winter weather pattern.
A lot of people don’t understand what El Niño (and its sister, La Niña) are and how they affect our weather. As you can imagine, the surface waters of our world’s oceans do not have the same temperature -- there are differences.
In the Pacific, when prevailing winds shift and push its warmer surface waters eastward toward the western side of South America, it’s called an El Niño. When those winds reverse and push those warmer surface waters westward toward Asia, it’s called La Niña.
So what’s the big deal about this? Because there is a tremendous interaction between our oceans and the atmosphere -- more thunderstorms form where those warmer waters are, and that impacts the jet stream configuration. And, as I’ve explained many times in the past, the jet stream not only separates cold air masses from warmer ones, but it’s also our general storm track.
In an El Niño winter, two things happen: The main Arctic jet stream tends to shift farther north, which limits Arctic air intrusions into our region. The farther north storm track sometimes gives us a drier than normal winter. El Niños also strengthen the subtropical jet stream, which creates a more persistent storm track across the south, and gives them a cooler, rainier winter in general.
In a La Niña winter, the Arctic jet stream trends farther south, allowing more Arctic blasts into the Great Lakes. If the storm track is near us, that means more snow storms.
Farther south, the subtropical jet stream is almost non-existent, so they have a drier, sunnier, more pleasant winter. If you’re a snowbird, you like La Niña winters.
Now that you understand El Niño, it’s time to update the winter outlook based upon some things we’ve observed recently. First and foremost, the developing El Niño appears to be a very weak one. When a strong El Niño develops, the winter forecast is easy: We are warm and dry here in southeast Michigan.
However, when the El Niño is weak, then other atmospheric and oceanic circulation patterns, such as the North Atlantic Oscillation and the Arctic Oscillation, become more important.
Right now, another oscillation, the Madden-Julian Oscillation, is in a phase that’s preventing the developing El Nino from “coupling” with the atmosphere -- this coupling is what leads to the jet stream shift that impacts our general winter weather.
Something else happening of great importance is that we are seeing indications potentially leading toward a sudden warming in the stratosphere -- not surprisingly, we call these events Sudden Stratospheric Warmings, or SSWs, and you should care about them because they impact the dreaded polar vortex. One notable expert on SSWs is Dr. Judah Cohen from Atmospheric and Environmental
Research, and he notes that “there are still questions of the magnitude of the SSW, and whether it will be a (polar vortex) displacement or a split.”
However, it appears more likely that a split will occur -- and this would suggest a return of colder air to the northeastern U.S., as well as potential significant winter storms.
Based upon the above, and the timing of the projected SSW, it appears that we’ll stay near to above average for temperatures into mid-January, after which, we’ll eventually see a trend toward colder and stormier weather for the last half of the winter. I’ll keep an eye on all of this, and update you if anything changes.
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