The latest update on El Nino from the U.S. Climate Prediction Center (CPC), issued Thursday, says the phenomenon is strengthening.  El Nino is the term used to describe the unusual warming of the surface water of the equitorial Pacific Ocean.  The warmer water causes weather patterns to shift around the world, sometimes with disastrous results.

Not all El Ninos (or La Ninas, the name for the atypical cooling of the equitorial Pacific) have dramatic effects on weather.  History (in weather terms, called climatology) has shown that the impact(s) of the phenomena are often dependent on location and strength.  Remember, the Pacific Ocean is a huge body of water, and usually, the warming doesn’t occur across the entire mass, but a portion of it.

The current El Nino is strongest in the central Pacific, where in October, sea surface temperatures were 1 to 1.5 degrees Celsius warmer than averge.  That’s a moderately strong El Nino.  The strongest El Ninos — which have produced the most catastrophic aftereffects — have temperature deviations of greater than two degrees Celsius. 

A moderately strong El Nino is historically correlated to certain weather outcomes in the United States, among them, warmer than average winters in the northern Plains and western Great Lakes.  Temperature patterns evident from analyzing the last 13 El Nino events (information available at the CPC’s El Nino site, if you want to see more) show the greatest effects in the northern Plains, beginning in December.  Here in West Michigan, the effects don’t typically begin to show until January, lasting through March.

As a result, I wouldn’t be surprised to see a continuation of the colder than average temperature pattern which began here in late September.  That might mean we get an early start to the snowfall, making it appear that we’re on the way to a cold and snowy winter.  But if history serves as an accurate marker, between January and March, the snowfall will be below average levels, as temperatures run slightly warmer than average.  By the way, you can read how my forecast stacks up against my TV competitors, and the climatological guru (Bill Marino) at the National Weather Service office in Grand Rapids, in the Sunday Grand Rapids Press.

Back to the CPC El Nino forecast.  The Thursday report from the CPC notes that forecast models (of which there are about a dozen) indicate the current El Nino will remain moderately strong (central Pacific equitorial sea surface temps about 1.25 to 1.50 degrees Celsius above average) through March.  After that time, the models show the phenomenon slowly disappearing, with surface water temps returning to normal/near normal levels by next summer.

One word of caution: the historical correlation between moderately strong and strong El Ninos and warmer winter weather is convincing, but not perfect.  There have been El Ninos that did not produce warmer winters.  But they are the exception to the rule.  Interestingly, a forecast for warmer winter temperatures in the northern Plains and Great Lakes goes against the Farmers Almanac forecast, which is for a very harsh season.  Time will tell!

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