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.
| 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
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.