What does ENSO mean to you? It sounds like it might be one of those acronyms beloved by the Pentagon or Homeland Security, doesn't it? It could stand for something like Enhanced National Security Options.
In fact though, ENSO stands for El Nino (La Nina) Southern Oscillation and it refers to a climate pattern that occurs across the tropical Pacific Ocean on a regular basis. It comes around on average every five years.
The variation that occurs in the surface temperature of the tropical eastern Pacific is known either as "El Nino" (warming) or "La Nina" (cooling). At the same time, the air surface pressure in the tropical western Pacific is known as the "Southern Oscillation." The two phenomena together create ENSO, and we need to understand ENSO because its effect on our weather is enormous, and as gardeners, we flourish or perish with the weather.
ENSO's effects are complicated and it affects weather right around the world, but let's try to at least understand what it does to us here in the southern part of North America.
During an El Nino period, winters in northeast Mexico and the southeast United States are cooler and wetter than average. It will not surprise you to learn that we were under the influence of El Nino last winter.
El Nino also tends to surpress hurricane activity which probably contributed to the fact that the 2009 hurricane season was the least active in twelve years. That El Nino period lasted through May 2010. Then La Nina took over.
For us, La Nina has mostly the opposite effect of El Nino. In North America, this means that the North Midwest, the Northern Rockies, Northern California, and the Pacific Northwest's southern and eastern regions all have above-average precipitation during La Nina, while right across the southern part of the continent - and that means us - below-average precipitation prevails. Also, in the southern part of the continent, warmer winters usually occur during La Nina.
Looking at the National Weather Service's Climate Prediction Center website today, I learned that the projection for November, December and January calls for above-average temperatures for our region and a continuation of below-median precipitation. If this is correct, we cannot look for an early end to our drought.
In fact, the NWS predicts that the La Nina period, with its dry conditions for the southern part of the country, will continue to hold sway until at least May of next year. Projecting beyond May is less reliable, they admit, but they believe that La Nina may be ending in the spring.
In my yard, we have experienced very little rain since July and the NWS certainly does not offer me any hope of real relief anytime soon. It looks like I might as well get used to moving sprinklers and hauling hoses around for the foreseeable future.
At the same time, if their predictions are correct, I might not be losing any plants to cold weather this winter, if only I can keep from losing them to dessication.
On the other hand, I've been seeing lots of woolly-bears lately and I have to tell you, they are all dark. Just like they were last fall when they predicted a cold winter for us. Who will be right this year - the scientists or the caterpillars?