Pacific El Niño strengthens; warmer winter in Michigan?

What does this mean for our upcoming winter?

DETROIT – Continued monitoring indicates that the ongoing El Niño in the Pacific Ocean will be one of the strongest on record, and this will have profound impacts on Michigan's upcoming winter, as I'll share with you later in this article.

You've heard me reference El Niño before, as well as its sister pattern, La Niña.

The concepts are pretty simple: In an El Niño, warmer-than-normal Pacific Ocean sea surface waters flow eastward while, in a La Niña, the opposite happens and those warmer waters flow westward, thus causing upwelling of cooler waters in the eastern Pacific.

So, what does this have to do with our weather?

Well, we meteorologists know that there is a tremendous interaction between various ocean circulation patterns and, since the jet stream (that band of strongest wind aloft) is both our winter storm track and the divider between milder temperatures to the south and colder temperatures to the north, you can now see that anything that changes the jet stream changes our winter weather. By the way, since some of you are bound to ask, El Niño/La Niña's impacts are not that strong in the summer because the jet stream is typically much farther north and not as much of a factor in our weather.

Impact on Hurricane season

El Niño has other impacts around the world, but one of the more prominent ones is on the Atlantic and Pacific hurricane seasons. Strong El Niños mean much reduced Atlantic hurricane activity, which is consistent with how the season has gone thus far, but enhanced hurricane activity in the Pacific, which we are also seeing. So, your friends and relatives in Florida can at least be comforted in knowing that there's a much smaller chance for a land-falling hurricane this season. Remember, though, that all it takes is one storm hitting the wrong place at the wrong time in an otherwise slow hurricane season (remember Hurricane Andrew?) to cause a disaster, so people down south and out east shouldn't let their guard down. But the odds of avoiding a hurricane are much higher this season.

Good news for California, too

For those people out west in drought-stricken California, development of a strong El Niño is great news because, at some point this winter, we'll see development of a "Pineapple Connection," which is a river of deep moisture bringing storm after storm into California. While there probably will be some devastating mudslides and the like, hopefully they'll be able to replenish some of the water in their reservoirs both through increased rainfall, and increased snowfall in the mountains (which is most important).

Impact in SE Michigan

Alright, what about a strong El Niño's impact on our upcoming winter here in southeast Michigan? The news is either very good or very bad, depending upon your outlook on winter.

Let's look back at two very strong El Niños: 1982-83 and 1997-98. Both of those winters were very warm, with significantly less snow than normal.

In the winter of 1982-83, we had a top-10 warmest and top-10 least snowiest December on record to start things off, and ended up with only 20.0 inches of total snow that winter (remember that our average winter snowfall is 42.7 inches). If you're old enough to remember that winter, as I am, you probably remember that record-setting 64 degrees high on Christmas Day! I also remember riding my bike to class at the University of Michigan on various days all winter long!

The winter of 1997-98 followed a very similar pattern: We had a top-ten warmest January and February, and only 22.0 inches of total snow that season.

If our current strong El Niño continues, then it would not surprise me to see a repeat of the winters of 1982-83 and 1997-98. However, there's one caveat: El Niño is not the only ocean circulation pattern we watch. The jet stream is impacted by that and others, and sometimes we don't understand some of the impacts.

As an example, let's examine the winter of 1972-73, which had another very strong El Niño.  That particular winter ended up with 45.0" of snow for us, with is very close to our long-term average.  However, that number doesn't tell the whole story:  we had above average snowfall in November and average snowfall in December and February, but only 2.4" total snow in January (a nice mid-winter break for those who didn't like snow). 

March had 10.1" of snow, but all of it came via a single, mid-month snowstorm…no snow fell on any other day that entire month.

This past winter is another good example:  there were a number of indicators suggesting that we wouldn't have a harsh winter, and look what happened.  So, while this winter's forecast is by no means a sure thing, the very strong El Niño at least gives increased predictability that we could be headed toward a milder, less snowy winter of 2015-2016.

Why are we seeing more 'extreme' weather?

While we're on the subject of the jet stream, there's one more thing I want you to know. You've all undoubtedly noticed the increase in extreme weather events across the country. You remember our record-setting snowfall in 2013-14; you remember Boston's record snowfall last winter; you remember the many extreme flood events that have hit various parts of the U.S. As Chuck Gaidica used to put it, we're seeing more "extreme extremes." But why?

Well, there's now an answer that is gaining wide acceptance by climate scientists. Global warming is weakening the jet stream which is, in turn, causing larger "mountains and valleys" (what we call a high index pattern) in the jet stream, and fewer flatter (what we call zonal) patterns. The reason is that, as the planet warms (and it IS warming), the higher latitudes are warming at a faster rate than the lower latitudes, as originally predicted by climate scientists many years ago. Since the strength of the jet stream usually results from the magnitude of the temperature difference from north to south, as the higher latitudes warm, there is less of a temperature difference. This periodically weakens the jet stream, and what results is the formation of deeper troughs and ridges ("mountains and valleys"). And since the stronger the trough-ridge combination is, the more extreme the resulting weather is, you can now see the connection.

I heard a fascinating presentation at an American Meteorological Society conference by the climate scientist who originated this theory, Dr. Jennifer Francis from Rutgers University, and if you were there with me and heard her in person, you'd agree: this makes perfect sense.

But is this weakening of the jet stream also impacting the strength of El Niño and La Niña? Only time will tell.