This winters hopes of an El Nino return appear to be fading. After a summer of hopeful predictions from the National Oceanic and Atmospheric Administration (NOAA) and elsewhere, the climate pattern that could save the western US and beyond from chronic, catastrophic droughts, may appear as barely a warm water whimper. NOAA now calls for about a two-thirds chance of weak El Nino atmospheric conditions. The key to everything in seasonal climate predictions is El Nino. This is true for land masses from Madagascar to Greenland; Earths rainmaking capabilities lie within slight temperature variations in the Pacific Ocean (less than a single degree even). Warmer than average temperatures constitute an El Nino event, while cooler temperatures give rise to the inverse phenomenon, La Nina. There are other large-scale climate phenomena on Earth that drive seasonal weather patterns, like the North Atlantic Oscillation, but nothing with as firm a grip as the El Nino/La Nina cycle, aka the El Nio Southern Oscillation. El Nino events have been few and far between lately, something thought to be at least in part a feature of climate change. Stronger winds pushing across North America from east to west, the result of Atlantic Ocean warming, act to churn up and mix Pacific surface waters, swapping warm surface waters for cooler, deeper waters. This absence is a crucial driver behind southwestern droughts. Water temperatures across the Pacific Ocean help determine the air pressure above, with warmer water resulting in lower air pressure and cooler water resulting in higher pressure. In an El Nino year, warmer water collects in the central and eastern Pacific. A lower atmospheric pressure region can be viewed as something like the bottom of a meteorological hill; weather will tend to roll downwards towards it. Normally the bottom of this hill would be found much farther to the east, creating a gradient across the Pacific that drives strong east-to-west trade winds, which carry moisture away from California lettuce fields. In an El Nino year, however, the bottom of the hill is shifted east and so is this gradient, with the result being a suppression of the moisture-stealing trade winds and, thus, of drought conditions. Related: After the Flood: A Photo Tour of Americas Drought-Stricken Reservoirs Climatologists started getting excited about a 2014/2015 El Nino all the way back in the springtime. Predictions were that this winter could be a major event, on par with the 1997/1998 winter that brought major flooding to California in one of the states wettest years on record. But, now, perhaps not so much, with the NOAAs Climate Prediction Center now calling for about a two-thirds chance of weak El Nino atmospheric conditions. Nothing is certain in a system as dynamic as Earths climate so, while warming waters offer some hope, they dont make promises. Usually the atmosphere starts responding to those temperature changes, but this year it didnt, David Pierce, a climate researcher at the Scripps Institution of Oceanography, told the New York Times. At this time, the consensus of forecasters expects El Nio to emerge during September-October and to peak at weak strength during the late fall and early winter, the NOAAs current El Nino discussion page reports. However, just as those early springtime predictions werent promises, neither is this. Seasonal climate predictions dont get much better than a roll of slightly loaded dice. California might get soaked yet.
Posted on: Wed, 10 Sep 2014 10:47:09 +0000
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