Wednesday, September 12, 2012

El Nino Update

The Climate Prediction Center (CPC) has issued an El Nino Watch as conditions are favorable for the development of a weak El Nino this fall.

In August, sea-surface temperatures were weakly above average across much of the equatorial Pacific Ocean (for example, see the so-called Nino3.4 region, which lies between 90–150ºW and 5ºS–5ºN), although the far eastern equatorial Pacific saw some areas of below average sea-surface temperature.

The development of above average sea-surface temperatures in the central and eastern equatorial Pacific is a hallmark of El Nino.  Nevertheless, the departures from average are small and atmospheric conditions in the tropics are not yet consistent with El Nino.  Convection remains primarily in the western equatorial Pacific (it typically shifts eastward during El Nino), and the easterly trade winds were near average (they typically weaken during El Nino).

For these reasons, the CPC classified August as ENSO-neutral (meaning no clear EL Nino or La Nina signal), but expects a weak El Nino to develop this month and persist through December–February.

As things stand now, I wouldn't change my winter ski plans based on this forecast.  The presence of a moderate or strong El Nino stacks the deck for a drier than average winter in the northwest and a wetter than average winter in the southwest (northern Utah is a toss up), but it appears this will be a borderline event.  The unpredictable random draw of weather and climate variability will probably play a dominant role in what happens this winter.  In other words, I haven't a clue what is going to happen this winter.

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