ENSO: a dry fall and winter?

According to the latest from the National Oceanic and Atmospheric Administration Climate Prediction Center, a weak El Niño continued during September 2009, as sea surface temperature anomalies remained nearly unchanged across much of the equatorial Pacific Ocean. Sea surface temperatures are the most important indicators for changes in the El Niño-Southern Oscillation cycle (abbreviated as ENSO). ENSO can be defined as anomalous warming in the eastern Pacific ocean; a reversal of oceanic surface temperature changes where the eastern pacific is relatively warm and the western pacific is relative cool. Like an engine warming, this action impacts the air (and water vapor) above it, sending currents of warm moist air in particular directions.

Courtesy of NOAA.

Courtesy of NOAA.

Expected El Niño impacts during this fall and early winter include more precipitation over the central tropical Pacific Ocean and drier-than-average conditions over Indonesia. For the lower 48 United States, potential impacts include above-average precipitation along the Gulf Coast and below-average precipitation for the Pacific Northwest. The Midwest could be warmer and drier than normal while the Southwest may get some above-average precipitation this winter.

But remember, these are all just predictions based on long-term trends, not on day to day forecasts of weather. Some El Niño years have seen monstrous storms delivered to our region, but overall, the trend is towards drier conditions.

According to the National Drought Monitor, the Northwest quadrant of Oregon is already abnormally dry. So the news of a predicted drier than average fall and early winter is not good for farmers, water providers, well owners and fish managers. Our relatively dry, mild fall weather is in keeping with this prediction, but again, nothing is completely certain when you are working with averages in climate prediciton, except that over time, this phase of ENSO tends to be drier than normal. Even so, keep your boots handy and your emergency supplies stocked.

The upside of this prediction is that for parched California, Texas and the desert Southwest, things might look up if the storms deliver their hoped-for payloads this fall and winter months.

“And it never failed that during the dry years the people forgot about the rich years, and during the wet years they lost all memory of the dry years.  It was always that way.” –John Steinbeck, East of Eden, 1952


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