What global sea surface temperatures resemble during an El Nino and La Nina winter
KMSP - You’ve heard this term many times before. Much like “polar vortex”, this nerdy meteorological term suddenly became mainstream back in the 90s when meteorologists were trying to explain why winter weather can vary so wildly from year to year. Mainstream enough, that Chris Farley on SNL had one of the most watched skits in the shows history… just google Chris Farley El Nino if you want a laugh.
El Nino is the term that refers to the warming of water in the Pacific Ocean around the equator. The warming of this water by just a few degrees Fahrenheit has global impacts because of the massive expanse of this phenomenon. Conversely, when ocean waters around the equator in the Pacific cool below average, then it’s called La Nina. If temperatures are close to average, then it’s considered neutral. Every stage of the Pacific Ocean has global consequences, whether it’s too cold or too hot or just “typical”.
But the same goes for many aspects of the world’s oceans. EL Nino was really the first time many meteorologists understood that the world’s oceans have patterns. We call them oscillations. The oceans will oscillate between relatively warmer and cooler temperatures, which is a major driver for the world’s weather. There’s El Nino, the Pacific Decadal Oscillation, the North Atlantic Oscillation, the East Pacific Oscillation, the West Pacific Oscillation, the Antarctic Oscillation, just to name a few. All of these are in different states for different periods and all have different impacts on our weather.
So now that you’re caught up, how will El Nino affect our weather this winter?
Well, as you would imagine, that’s a complex question that we can only guess the answer. Just like everything else in weather, no two events are ever the same. Some might be similar, but they are NEVER exactly the same. El Nino and La Nina are no different. The strength of El Nino (how far above average the water temperatures are) plays just as much of a role as everything else. There are two pictures in the slideshow above that show how far above and below average precipitation and temperature are across the country during every El Nino since 1950. They are also separated into 3 different classifications: strong, moderate, and weak. Strong El Nino’s have Pacific Ocean temperatures the farthest above average and weak El Nino’s have Pacific Ocean temperatures just slightly above average. The big thing to note, is just how different each year can be.
For example, strong El Nino’s generally have very wet conditions in parts of the west coast and the south. But notice that the exact locations of the very wet conditions change from each year. The strong El Nino of 1982-83 brought very heavy precipitation to Louisiana, Mississippi, and the Pacific Northwest, but the very next one in 1997-98 brought very heavy precipitation to California, Florida, and the Carolinas. Again, it stays in the general areas of the west coast and the south (at least in years past), but changes specific locations. But even then, other areas break the rules. 1972-73 brought near normal precipitation to much of the country. When you get to weaker El Ninos, temperature and precipitation vary even more widely ranging from exceeding dry and cold years like 1976-77 to a wide array of temps and precip nationwide.
So the simple answer to our winter question is we don’t really know. BUT, we can extrapolate a possible forecast based off of how strong we anticipate our El Nino to be as well as analyze our fall weather to see how we’ve faired in years past.
The forecast for the strength of our El Nino is in an image above. It’s a graph that shows each individual computer forecasting model’s forecast for sea surface temperatures based off of 3 month averages. Above the middle black line, and temperatures are expected to be above average. Below it, they are likely to be below average. So far this fall, temperatures have been about a half degree Celsius above average, considered to be a weak El Nino. If temperatures get a degree above average, it’s considered a moderate El Nino. Then when they get close to 2 degrees above average, it’s a strong El Nino.
If you are to average all of the computer model’s forecasts out, then our El Nino will likely be close to a moderate one where sea surface temps are about a degree above the average. There have been a few other moderate El Nino’s since 1950. So I compared fall temperatures and precipitation of those years to what we have experienced over the last couple of months… the very wet and cool conditions we have seen since September started.
Amazingly, 2002 was a similar year. A very wet and cool September and October along with a similar strength El Nino to what is expected this winter. So when looking at temperatures and precipitation from the winter of 2002-03, Minnesota experienced a slightly warmer than average and drier than average winter. While our upcoming winter could vary wildly from what happened in 2002, I think we have a pretty good shot at ending up with something similar. Now, I want to remind you that this forecast is only for the WINTER months of December, January, and February and does not include all of our cold and snow season, that can extend into April as we saw last season. But definitely gives us an idea of what we are more likely to experience in the coming months.