Enter El Nino & The Blob
An El Nino is already in progress, and it’s looking like a pretty good one. Sea surface temperature anomalies in the Nino 3.4 region have been above 0.5°C for seven of the last eight 3-month periods, and it currently sits at a very respectable +1.0°C. For reference, 1.0°C is the highest May/June/July positive anomaly since 1997 – which you may remember as the beginning of the strongest El Nino we’ve ever measured (1997/1998).
The current SST anomalies across the globe (Figure 1, top) do look strikingly similar to how they did in August of 1997 (Figure 1, bottom). Two things that are different are 1. the SST anomalies along the equator in the east Pacific are not currently as extreme as in 1997 and 2. An area of very warm water off the Pacific Northwest coast, which has been named “The Blob,” is much warmer and much larger this year than in 1997.
So, what’s going to happen? In short, we don’t know, exactly. First, we have to forecast the evolution of El Nino correctly. Second, the actual weather that results from each El Nino isn’t always the same. And, third, we aren’t sure what affect The Blob might have on all of this, because we haven’t really seen such a large Blob before.
The Evolution of El Nino
The track record of predicting the state of ENSO in the future isn’t perfect. What long range forecast is? The latest model forecasts predict a strong El Nino lasting into 2016, all experts seem to agree on some version of this scenario, and it sure looks like it to me.
What Will The Weather Do?
If we believe these El Nino forecasts, and I do, the next challenge is to say what that means. Unfortunately, the news isn’t really better on that front. Because no two El Ninos are ever the same, and because the effects of El Nino on the global circulation pattern (and vice versa) are so complex, there is really nothing we can say, specifically.
For example, despite the common belief that El Ninos are always stormy and wet and California, it isn’t always so. To see what I mean, consider the following charts, which show the precipitation patterns that have resulted from all El Ninos we’ve measured.
See? It isn’t the same for all El Ninos, not even for all strong El Ninos. What we can say is that most El Ninos are wet and stormy in California, but not all. The NWS Climate Prediction Center said it well in their latest ENSO post: “El Nino ’tilts the odds’ for weather and climate impacts.” Which is to say that it tilts the odds that we’ll see impacts like this:
What About Blob?
This is where it gets interesting. I plan to flesh this out in a following post, but recent research from my alma mater, the University of Washington, suggests that The Blob is caused by persistent high pressure over the northeast Pacific which is caused by abnormally high water temperatures in the tropical west Pacific. Unusually warm water was present in the west Pacific last winter as the Blob formed.
This has interesting implications, because if this El Nino evolves like its evil twin from 1997, the warm water in the tropical west Pacific may disappear, which should cause The Blob to disappear. It did in 1997. Here is the SST anomaly from Dec 30, 1997:
You can see that by the end of 1997, the Blob was completely gone and had been replaced by cooler than normal SSTs over the entire NE Pacific. Furthermore, the waters in the tropical west Pacific had also cooled below normal, which was almost certainly an artifact of the development of the strong El Nino in 1997/1998.
If this happens again this time, we might be able to expect impacts from this El Nino like the ones we saw in 1997. Precipitation anomalies from 1997/98 El Nino are shown in Figure 5, below. Unfortunately, I don’t have SST data from the 1982/83 El Nino. It was also a very strong El Nino, and I’d sure like to compare it to our current situation, because that one was outlandishly wet up and down the Pacific Coast.
Of course, the destruction of the The Blob in 1997/1998 is no assurance that it will happen the same way this time. After all, The Blob is much more pronounced this year than back in 1997. I’m just saying that there are reasons to think it could happen this way again. This also has implications for the eastern part of our continent which was ravaged by cold and snow over the last couple of winters. I’ll explain my theory on this in my next post.
What About The Pacific Northwest?
Unfortunately, there is no clear signal for what to expect in the Pacific Northwest during an El Nino. As we saw in Figure 2 (above), precipitation in the PacNW can vary from very wet to very dry, even during strong El Ninos. I’ve poured over rainfall/snowfall records for many locations from California to BC, and below is a bullet list of the most interesting things I found.
We are in the midst of a developing strong El Nino. Conditions right now are very similar to August 1997, which was the strongest El Nino that we’ve ever measured. Because no two El Ninos are exactly alike and The Blob may complicate things, we can’t say exactly what will happen. But the scales should be tipped toward wet weather across the southern U.S. this winter, with warmer than normal weather to the north. In the north, precipitation could amount to anything.
Interesting Things I Found From Past El Ninos
I’ve analyzed climate data from many sites over the western U.S. back to 1950 (the period for which I have SST data to compare to). Here are some of the things I found interesting:
- Seattle, Portland, and Medford get much less snow during El Ninos than non El Nino years, especially since 1982 (what I call the modern era). Prior to 1982, they got a lot more snow overall, including during El Nino years.
- In the modern era, Medford, OR has gotten only 1.5 inches of snow during all strong El Nino years combined. In non-El Nino years during the same period, they’ve averaged almost 4 inches per year. Prior to 1982, Medford did have some above average snow years during El Ninos.
- Seattle, WA* averages just 1.6 inches of snow during El Nino years and 6.7 inches in non El Nino years in the modern era. During strong El Ninos, it’s even worse with an average of just 0.8 inch.
- Ironically, the biggest snow season since 1950 in Seattle* occurred during the 1968-69 El Nino. I was born in Seattle, during this season!
- Portland, OR has averaged just 1.1 inches of snow during modern era El Ninos versus 6.0 inches during non El Nino years. They also haven’t received any snow during strong El Ninos in the modern era.
- Spokane, WA has received an average of 25.1 inches of snow during all El Ninos in the modern era. This is less than half of the average during non-El Nino years in the same period (51.8″).
- Snowfall in the mountains during El Ninos is generally much less than during non El Nino years in the north. As we move south, the difference diminishes until it’s basically gone in California. See the following chart. I didn’t get a chance to look for mountain locations further south, but I suspect I’d find a reversal of that trend.
I get these records from the Western Regional Climate Center. I do the math myself.
*This is based on a reconstruction I made of Puget Sound snowfall. In the decade between roughly 1997 and 2007, climate records for Western Washington (snow record, in particular) are very sketchy to non-existent. I have no idea why the records are missing, but I made my own record using a composite of records from around the area. See here for more details.