Will 2015-16 Be a Winter to Remember?
Strong El Niño Likely to Cause Extreme Conditions

By Dave Carr
Director, Blandy Experimental Farm

By now everyone has heard that a strong El Niño is developing in the Pacific Ocean.  These events are part of the cyclical temperature changes in the equatorial waters of the Pacific.  The period of the oscillation from warm El Niño to cool La Niña and back again is irregular, and the magnitude of the temperature fluctuation varies considerably from event to event.  In years when an El Niño develops, people usually begin to notice the effects sometime near Christmas (hence the name, the “baby boy”).  There have been four El Niño events since 2002, but these were all fairly mild.  The El Niño that’s shaping up for this winter appears to be the strongest since at least the winter of 1997/98, as measured by sea surface temperature in that region.

So what will this mean for our area, thousands of miles from the equatorial Pacific?  The winter of 1997/98 was my first here at Blandy, and the El Niño actually made it quite memorable.  Thanks to Bob Arnold’s meticulously collected weather data, it is easy to see how that winter stacked up against a typical northern Shenandoah Valley winter.

 
https://sites.google.com/site/blandyvirginia/arboretum/el-nino/weatherdata.png
 Click the chart for historical weather data.
The fall of 1997 started off with a very typical September and a drier than normal October, but temperatures both months were very seasonal.  November high temperatures were about 5° F cooler than normal, but the low temperatures were very close to seasonal averages.  The cooler than normal highs were largely due to periods of cool wet weather, as the monthly rainfall (8.7 inches) was 2.6 times higher than average.  This rain foreshadowed things to come.

After a very average December that ended with 7 inches of snow on the 30th, the full effects of El Niño appeared as the calendar turned to 1998.  That January and February period was the mildest of my entire 18-year career at Blandy.  January high and low temperatures both averaged more than 6° F above normal.  February highs averaged only 3.3° F above normal, but the average low that month was nearly 7° F above normal.  The mercury fell below freezing only 18 nights in January and only 12 nights in February.  Along with the mild temperatures came the rain.  The 7.9 inches of precipitation in January was more than three times normal, and almost all of it fell as rain.  February precipitation was 2.5 times higher than normal, and except for 4 inches of wintery mix on the 4th, it was almost all rain.

By March, the temperatures and rainfall were basically back to normal, and the weather continued that way through the spring as the El Niño weakened.  The effects of that winter were evident well into the summer, however.  All told, the 24.5 inches of precipitation from November through February was 2.3 times the normal level.  The water table rose over 10 feet during the winter, and all of the ponds at Blandy overflowed by spring, essentially dividing Blandy in half.  It was often impossible to walk from the north half of Blandy to the south half without getting your feet wet.  Lake Georgette, the little pond south of the Quarters, filled the entire grassy field to the east, while Rattlesnake Spring often flooded the old loop road, forcing its closure.  I saw more species of ducks at Blandy that spring than I have seen since.  The water table has approached these heights only a couple of years since (following Hurricane Isabel in 2003 and the “Snowmageddon” winter in 2009/10), but neither surpassed the heights of the 1998 El Niño.

So what can our region expect from this coming El Niño?  Well, by mid-November, the measurement of El Niño strength (the “Oceanic Niño Index” or ONI) surpassed the highest recorded ONI for the 1997/98 event.  If the high sea-surface temperatures are sustained for another couple of months, the 2015/16 El Niño will supplant the 1997/98 event as the champion of all El Niños.  Should we expect a repeat of the warm, wet winter we saw back then?  Meteorologists and atmospheric scientists seem to be cautious about their predictions, pointing out that the planet is much warmer overall than it was in 1998.  How record warming in the Pacific will play out globally under these extreme conditions is difficult to say.  For better or worse, I’m betting that it will be another winter to remember.