'Super' El Niño favors milder, less snowy winter for Minnesota

Our Friday cold front leaves little doubt that the seasonal transition is underway in Minnesota.

As we look ahead to winter, one major factor is likely to drive our overall winter conditions. A moderate to strong to very strong El Niño is brewing in the tropical Pacific Ocean. That extra warm ocean water thousands of miles from Minnesota statistically produces milder and less snowy winters compared to long-term averages.

We still get winter in Minnesota during El Niño years. We still get snow. We still get subzero temperature outbreaks.

But when you add it all up over the course of a season? We’ll likely feel like this upcoming winter is a bargain compared to last winter’s 90-inch snow blitz in the Twin Cities.

Super El Niño?

El Niño is a state of abnormally warm water in the tropical Pacific Ocean. The magnitude of warming above average indicates the level of El Niño.

So what is a Super El Niño? While the term is not an official category used by the National Oceanic and Atmospheric Administration, it is often used by meteorologists to describe the strongest level of El Niño.

Frankly, it’s more conversational than “historically strong.” I mean, we have supermoons, so why not Super El Niño’s?

Here is a great description of the thresholds for different El Niño classifications from the Minnesota State Climatology Office (my italics):

An El Niño becomes official when ocean temperatures in the  "Niño 3.4 region opens in a new browser tab" remain at least 0.5 degrees C  (0.9 F) above recent 30-year averages for five consecutive three-month periods.

An episode is identified as "moderate" if any three-month period is at least 1.0 C (1.8 F) above average, and "strong" if it reaches 1.5 degrees C (2.7 F) above average. NOAA's Climate Prediction Center calls an episode "historically strong" (others use the term "very strong") if the Niño 3.4 region reaches 2.0 C (3.6 F) above average.  

Of the 25 El Niño episodes since 1950, six have been moderate, four have been strong, and five have been very strong or historically strong. The most recent very strong episode was in 2015-16, which is considered to be the strongest El Niño on record.

So under my terminology in this post, a Super El Niño event correlates to sea surface temperature anomalies of at least 2.0 C above average. 

Forecast

Sea surface temperatures are already well above average in the tropical Pacific Ocean. The latest weekly Niño index values range from 1 degree to 2.6 degrees Celsius above average in different regions. So we’re already officially in moderate to Super El Niño territory across the tropical Pacific basin.

Model forecasts for this upcoming winter range center around a strong El Niño event, but several models produce sea surface temperatures greater than +2.0 C this winter. I’ve highlighted those on the chart below.

So a strong to historically strong Super El Niño event is likely this winter.

Here’s NOAA’s latest look at the odds:

“the team favors at least a “strong” event with a 75-85% chance through November-January (>/=1.5C) for the seasonal average in Niño-3.4. There is a 3 in 10 chance of a “historically strong” event that rivals 2015-16 and 1997-98 (seasonal average >/= 2.0C).”

Impact on Minnesota?

There’s a strong correlation between milder and less snowy than average weather for Minnesota during El Niño winters. Overall the correlation is about 70 to 80 percent for milder-than-average winters and less snow.

El Nino winters average about 1.8 degrees warmer overall for Minnesota. They also produce about 22 percent less snowfall (12.7 inches less) in the Twin Cities compared to long-term averages.

Here’s a good summary of the impact of El Niño winters on Minnesota from The Minnesota State Climatology Office.

In Minnesota, El Niño conditions have tended to produce mild winters with less snow than average.  The 25 El Niño winters since 1950 averaged 1.8 degrees F warmer on a statewide basis than non-El Niño winters, and have produced an average of 22% less snow (12.7 inches) in the Twin Cities.

The warmest December-through-February on record in Minnesota came during the very strong 1997-98 El Niño episode. The very strong events in 2015-16 and 1982-83; the strong El Niño in 1991-92; and the moderate one in 1986-87, also are associated with winters that are among Minnesota's 10 warmest on record. 

So the odds strongly favor a milder-than-average winter in Minnesota with less-than-average snowfall.

Stay tuned.