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Winter '16 / '17 - Snowfall Forecast Contests
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Wednesday, December 20, 2006

Implications of Region 3.4/s Latest SSTA - Is el Nino Fading?

This week/s Nino 3.4 region SSTA comes in @ 1.3°C....down 7% from last week.

Is this the beginning of the end? Did it ever get started?

About a year ago...NOAM countries reached consensus on an operational definition for what conditions constitute 'el Nino' and his evil little sister.

"The index is defined as a three-month average of sea surface temperature departures from normal for a critical region of the equatorial Pacific (Niño 3.4 region; 120W-170W, 5N-5S)."
[...]
El Niño: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5 degrees C (0.9 degrees Fahrenheit), averaged over three consecutive months."

Nino 3.4 region SSTAs "averaged over three consecutive months" which means there/s a lag built into the calculation. El Nino conditions don/t suddenly appear one day when the SSTA reaches 0.5°C and nor does it fade when an observation falls below the threshold.

The '06 el Nino began toward the end of September when the 12-week SSTA moving average breached 0.5°C. The first observation of an SSTA above the definition/s threshold occurred about six weeks earlier.

The el Nino reached moderate strength (> 1°) with the December 6 observation and continues at the same strength this week...even though the current SSTA declined 7% from last week. In fact...the 12-week moving average rose from 1.01°C to 1.05°C.

Even if the Nino 3.4 region SSTA came in @ 0°C each week for the next two months...el Nino conditions would continue until the first week of February.

How likely is it to see such a sharp drop off of SSTAs? Not very.


Heavy bars bracket Region 3.4


Granted...growth in SSTAs may be slowing or it may simply be evidence of a wave passing through the region. The index has been growing 6 - 9% / week but only 4% with the latest datum. Upstream...in Region 4...SSTAs have held steady @ 1.3°C the past four weeks.

Is it the beginning of the end?

Despite some buzz to the contrary...it/s doubtful. It/ll take some time for the region 3.4/s SSTA to decay.

Did it ever get started?

That seems doubtful...too. At least as far as the planetary flow regime over the CONUS is concerned...although the progs the past few days seem to be coming around to a pattern more representative of +ENSO.

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